Operators in php
1. Assignment operator
2. Arithmetic operator
3. Comparison operator
4. String operator
5. Increment operator
6. Logical operator (exclusive OR operation xor)
7. Ternary operator
8. Bit operator (shift operation)
10. The difference between ',' and '.' in echo
9. Type conversion
1). Boolean value - string
2) . String - Conversion of numbers
3). String - Conversion of Boolean values
4). Numbers - Conversion of Boolean values
5). Numbers - Conversion of strings
Control structure
1. if single-way branch
2. if /else double-way branch, the two code segments in if/else in the double-way branch must have and only one section is executed
if/else if/else if.../else multi-way Branch
3. switch case, which is convenient for comparing multiple possible values of the variable being judged.
4. while (expression){
code segment}
5. do{
code segment;}while(expression);
6. for(statement 1; statement 2; statement 3) {
code segment ;}
Statement 1, execute first and only once
then judge statement 2, if it is true, execute the code segment;, then execute statement 3;
then judge statement 2...loop
until statement 2 is false, for end
Code display
<span> 1</span><span>//</span><span>==========================================
</span><span> 2</span><span> 3</span><span>//2. 算术运算 </span>返回原处
<span> 4</span><span>//
</span><span> 5</span><span>//php程序如何进行加减乘除
</span><span> 6</span><span>//依次是+ - </span><span> 7</span><span> 8</span><span> 9</span><span>$a</span> = 3<span>;
</span><span> 10</span><span>$b</span> =5<span>;
</span><span> 11</span><span>$c</span> = <span>$a</span> + <span>$b</span>;<span>//</span><span>这语句话的含义是$a+$b计算结果赋给$c</span><span> 12</span><span>echo</span><span>$c</span>,'<br />'<span>;
</span><span> 13</span><span>echo</span><span>$b</span>-<span>$a</span>,'<br />'<span>;
</span><span> 14</span><span> 15</span><span>echo</span><span>$a</span> * <span>$b</span>,'<br />';<span>//</span><span>计算$a * $b的结果 赋给$c </span><span> 16</span><span>echo</span><span>$b</span>/<span>$a</span>,'<br />';<span>//</span><span>计算$b/$a的结果，赋给$c
</span><span> 17</span><span> 18</span><span>//如果是在C语言中，$b,$a,都是整型，因此计算出来的$c也是整型
</span><span> 19</span><span>//在php中，变量的值可以随意改变，而且变量的类型也可以改变。
</span><span> 20</span><span>//
</span><span> 21</span><span>//比如：变量$c是整型，可以突然为之赋一个浮点型值。
</span><span> 22</span><span>//因此php称为动态语言。
</span><span> 23</span><span> 24</span><span> 25</span><span> 26</span><span> 27</span><span>//-----------------------------------------------------</span><span> 28</span><span>求余就是 取模 运算 返回原处
</span><span> 29</span><span>在计算机里计算除法的时候，算出来2个结果
</span><span> 30</span><span> 31</span><span>商和余数
</span><span> 32</span><span> 33</span> */
<span> 34</span><span>$a</span> = 3<span>;
</span><span> 35</span><span>$b</span> = 5<span>;
</span><span> 36</span><span>$c</span> = <span>$b</span>%<span>$a</span>; <span>//</span><span> 得1 余2</span><span> 37</span><span>echo</span><span>$c</span>,'<br />'<span>;
</span><span> 38</span><span> 39</span><span> 40</span><span>//</span><span>小测试，判断一个数是偶数，还是奇数?
</span><span> 41</span><span>//可以对2 取模，余数是1，则为奇数，如果余数为0,则为奇数</span><span> 42</span><span> 43</span><span>$d</span> = 3<span>;
</span><span> 44</span><span>$res</span> = <span>$d</span> % 2<span>;
</span><span> 45</span><span>if</span>(<span>$res</span> == 1<span>){
</span><span> 46</span><span>echo</span><span>$d</span>,'是奇数'<span>;
</span><span> 47</span><span>}
</span><span> 48</span><span>if</span>(<span>$res</span> == 0<span>){
</span><span> 49</span><span>echo</span><span>$d</span>,'是偶数'<span>;
</span><span> 50</span><span>}
</span><span> 51</span><span> 52</span><span>//</span><span>上初中了，有了负数的概念</span><span> 53</span><span> 54</span><span>$b</span> = -5<span>;
</span><span> 55</span><span>$a</span> = 3<span>;
</span><span> 56</span><span>echo</span><span>$b</span>%<span>$a</span><span>;
</span><span> 57</span><span>$b</span> = -5<span>;
</span><span> 58</span><span>$a</span> = -3<span>;
</span><span> 59</span><span>echo</span><span>$b</span>%<span>$a</span><span>;
</span><span> 60</span><span> 61</span><span>//</span><span>注意：在取模运算的时，
</span><span> 62</span><span>//运算的正负结果，取决于被除数的符号
</span><span> 63</span><span>//结果的符号，和被除数的符号一致
</span><span> 64</span><span>//================================================
</span><span> 65</span><span> 66</span><span> // 比较运算符 返回原处
</span><span> 67</span><span>// > ,< ,<= ,>= ==,!= ,===(不仅值相等，而且类型也相等),!==</span><span> 68</span><span>$a</span> = 3<span>;
</span><span> 69</span><span>$b</span> = 2<span>;
</span><span> 70</span><span>if</span>(3 > 2<span>){
</span><span> 71</span><span>echo</span> '3大于2','<br />'<span>;
</span><span> 72</span> }<span>else</span><span>{
</span><span> 73</span><span>echo</span> '3不大于2','<br />'<span>;
</span><span> 74</span><span>}
</span><span> 75</span><span> 76</span><span>if</span>(<span>$a</span> >= <span>$b</span>){ <span>//</span><span> >= 意味着，$a比$b大，或者 $a 等于$b 有一个为真都行，即条件满足 </span><span> 77</span><span>echo</span> '3大于等于2','<br />'<span>;
</span><span> 78</span> }<span>else</span><span>{
</span><span> 79</span><span>echo</span> '3并不大于等于2','<br />'<span>;
</span><span> 80</span><span>}
</span><span> 81</span><span>//</span><span>-----------------------------------------------</span><span> 82</span><span> 83</span><span>$a</span> = 3<span>;
</span><span> 84</span><span>$b</span> = '3'<span>;
</span><span> 85</span><span>if</span>(<span>$a</span> === <span>$b</span><span>){
</span><span> 86</span><span>echo</span><span>$a</span>,'全等于',<span>$b</span>,'<br />'<span>;
</span><span> 87</span> }<span>else</span><span>{
</span><span> 88</span><span>echo</span><span>$a</span>,'不全等于',<span>$b</span>,'<br />'<span>;
</span><span> 89</span><span>}
</span><span> 90</span><span> 91</span><span>//</span><span>==========================================</span><span> 92</span><span> 93</span><span>$a</span> = 3<span>;
</span><span> 94</span><span>$b</span> = <span>true</span><span>;
</span><span> 95</span><span>if</span>(<span>$a</span> == <span>$b</span><span>){
</span><span> 96</span><span>echo</span><span>$a</span>,'等于',<span>$b</span>,'<br />'<span>;
</span><span> 97</span> }<span>else</span><span>{
</span><span> 98</span><span>echo</span><span>$a</span>,'不等于',<span>$b</span>,'<br />'<span>;
</span><span> 99</span><span>}
</span><span>100</span><span>//</span><span>在不同的类型比较时
</span><span>101</span><span>//php程序本身
</span><span>102</span><span>//
</span><span>103</span><span>//会把变量 转换成一致的类型，然后再去比较
</span><span>104</span><span>//
</span><span>105</span><span>//着重记以下转换 返回原处
</span><span>106</span><span>//1. 布尔值 －－字符串
</span><span>107</span><span>//2. 字符串 －－ 数字的转换
</span><span>108</span><span>//3. 字符串－－ 布尔值的转换
</span><span>109</span><span>//4. 数字 － － 布尔值的转换
</span><span>110</span><span>//5. 数字 －－字符串的转换
</span><span>111</span><span>//
</span><span>112</span><span>//以5 ＝＝true 比较为例
</span><span>113</span><span>//的把 整型 ，转成布尔型
</span><span>114</span><span>//
</span><span>115</span><span>//其实有的语言中，根本就没有布尔型，都是拿1，0充当true / false
</span><span>116</span><span>//0 / 0.0 这两个转换为布尔类型为false
</span><span>117</span><span>//其他都是true ，负数也是true
</span><span>118</span><span>119</span><span>120</span><span>121</span><span>122</span><span>//-------------------------------------------
</span><span>123</span><span>//1. 布尔值 －－字符串</span><span>124</span><span>true</span> ---'1'
<span>125</span><span>false</span>--- ''
<span>126</span><span>127</span><span>//</span><span>-------------------------------------------
</span><span>128</span><span>//1. 字符串 －－数字的转换
</span><span>129</span><span>//从字符串左端开始找数字，直到第一个非数字结束，取出来的这一部分，即是转换后的值
</span><span>130</span><span>//'3q'----3</span><span>131</span> '123asdf'---123
<span>132</span> 'sdfds789'----0
<span>133</span><span>134</span><span>$num</span> = 'sdfds789'<span>;
</span><span>135</span><span>echo</span><span>$num</span> + 0; <span>//</span><span>运算结果是0
</span><span>136</span><span>137</span><span>//-------------------------------------------
</span><span>138</span><span>//3. 字符串 －－布尔的转换
</span><span>139</span><span>//''字符串，'0'，这种转换成 false
</span><span>140</span><span>//其他的一概是true</span><span>141</span><span>142</span><span>143</span><span>144</span><span>if</span>(''==<span>false</span><span>){
</span><span>145</span><span>echo</span> '空字符串等于false'<span>;
</span><span>146</span> }<span>else</span><span>{
</span><span>147</span><span>echo</span> '空字符串不等于false'<span>;
</span><span>148</span><span>}
</span><span>149</span><span>150</span><span>echo</span> '<br />'<span>;
</span><span>151</span><span>if</span>('0'==<span>false</span><span>){
</span><span>152</span><span>echo</span> '字符串0等于false'<span>;
</span><span>153</span> }<span>else</span><span>{
</span><span>154</span><span>echo</span> '字符串0不等于false'<span>;
</span><span>155</span><span>}
</span><span>156</span><span>157</span><span>158</span><span>//</span><span>-------------------------------------------
</span><span>159</span><span>//4. 字符串 －－布尔的转换
</span><span>160</span><span>// 只有整型的0 ，和浮点的0.0 ，转换false
</span><span>161</span><span>//其他 ，甚至负数 ，也转换成true
</span><span>162</span><span>163</span><span>164</span><span>165</span><span>//-------------------------------------------
</span><span>166</span><span>//5. 数字 －－字符串的转换
</span><span>167</span><span>//直接是字面本身 </span><span>168</span><span>echo</span> '<br />'<span>;
</span><span>169</span><span>echo</span> 'aaa'. 2323<span>;
</span><span>170</span><span>171</span><span>172</span><span>173</span><span>//</span><span>-------------------------------------------
</span><span>174</span><span>//字符串 返回原处
</span><span>175</span><span>176</span><span>//在php中字符串，有一句运算，就是拼接 (echo中','和'.' 的区别)</span><span>177</span><span>178</span><span>$str1</span> = 'hello'<span>;
</span><span>179</span><span>$str2</span> = ''<span>;
</span><span>180</span><span>181</span><span>$str3</span> = 'world'<span>;
</span><span>182</span><span>echo</span><span>$str1</span>.<span>$str2</span>.<span>$str3</span><span>;
</span><span>183</span><span>echo</span><span>$str1</span>,<span>$str2</span>,<span>$str3</span><span>;
</span><span>184</span><span>185</span><span>//</span><span> 新手的疑问 </span><span>186</span><span>187</span><span>echo</span><span>$str1</span>.<span>$str2</span>.<span>$str3</span><span>;
</span><span>188</span><span>//</span><span>这一行是$str1,$str2,$str3在内存中拼接运算
</span><span>189</span><span>//运算出一个'hello world'一个大字符串，
</span><span>190</span><span>//然后echo 之，得到判断的结果 hello world
</span><span>191</span><span>//==========================================</span><span>192</span><span>193</span><span>echo</span><span>$str1</span>,<span>$str2</span>,<span>$str3</span><span>;
</span><span>194</span><span>//</span><span>echo 是个语句，负责输出用的
</span><span>195</span><span>//可以通过','分割 一次输出多个变量或值来
</span><span>196</span><span>//
</span><span>197</span><span>//综上：
</span><span>198</span><span>//用' . '是先拼接，再整个输出
</span><span>199</span><span>//用' , ' 是挨个儿把3个变量输出。
</span><span>200</span><span>//
</span><span>201</span><span>//面试时，会碰到 会问法：
</span><span>202</span><span>//用' . '，用' , '那个输出的快，效率高
</span><span>203</span><span>//
</span><span>204</span><span>//答：当然是 ',' 输出快，效率高</span><span>206</span><span>//==========================================
</span><span>207</span><span>//赋值运算符，就是 ＝ ，作用是，把‘=’右边的值，赋给左边变量 <span>返回原处</span></span><span>208</span><span>$a</span> = 3<span>;
</span><span>209</span><span>$b</span> = <span>$c</span> = 5<span>;
</span><span>210</span><span>211</span><span>212</span><span>//</span><span>==========================================
</span><span>213</span><span>//运算符的运算结果
</span><span>214</span><span>//
</span><span>215</span><span>//大家想：既然是运算，运算完之后，必须得有一个结果 －－－结果值
</span><span>216</span><span>//3 + 2; 运算结果5
</span><span>217</span><span>//
</span><span>218</span><span>//1. 比较运算符 返回原处
</span><span>219</span><span>//注意 ：比较去处符返回结果，，只有2个可能 true/false
</span><span>220</span><span>//
</span><span>221</span><span>//以$a =＝ $b 为例，，要么等，要么不等
</span><span>222</span><span>//要么是真，要么是假
</span><span>223</span><span>//2 ＝＝3；运算结果是：false
</span><span>224</span><span>225</span><span>//==========================================
</span><span>226</span><span>//2. 字符串运算符 返回原处
</span><span>227</span><span>//字符串运算符
</span><span>228</span><span>//$a.$b
</span><span>229</span><span>//返回结果：拼接后的结果
</span><span>230</span><span>231</span><span>//==========================================
</span><span>232</span><span>//赋值运算符，返回值是多少呢？</span><span>233</span><span>$a</span> = 3<span>;
</span><span>234</span><span>if</span>(<span>$a</span> = 33<span>){
</span><span>235</span><span>echo</span> 'aa'<span>;
</span><span>236</span> }<span>else</span><span>{
</span><span>237</span><span>echo</span> 'bb'<span>;
</span><span>238</span><span>}
</span><span>239</span><span>//</span><span>赋值运算长符的运算结果，就是 ＝右边的值 </span><span>240</span><span>$a</span> = <span>$b</span> = <span>$c</span> =88
<span>241</span><span>//</span><span>过程是这样的， $b = 88先进行，赋值后返回88
</span><span>242</span><span>//返回的88，再赋给$c
</span><span>243</span><span>//同理 ……
</span><span>244</span><span>//最终$a也赋值为88
</span><span>245</span><span>//
</span><span>246</span><span>//
</span><span>247</span><span>//两个难点；
</span><span>248</span><span>//1. 比较运算时，有一个类型转换的问题
</span><span>249</span><span>//2. 凡运算，必有返回值
</span><span>250</span><span>//比较运算返回布尔值
</span><span>251</span><span>//
</span><span>252</span><span>//赋值运算，返回赋的值本身
</span><span>253</span><span>254</span><span>//==========================================
</span><span>255</span><span>//6. 逻辑运算符 返回原处
</span><span>256</span><span>//
</span><span>257</span><span>//命题：
</span><span>258</span><span>//真命题，假命题
</span><span>259</span><span>//
</span><span>260</span><span>//逻辑运算符：逻辑或 || or
</span><span>261</span><span>//逻辑与 && and </span><span>262</span><span>263</span><span>$house</span> = 180<span>;
</span><span>264</span><span>$car</span> = 'BYD'<span>;
</span><span>265</span><span>266</span><span>//</span><span>$res = $house && $car == 'BMW'如果这样写，谁先给结合 ，牵涉到运算优先级的问题
</span><span>267</span><span>//我们推荐，在多个量进行去处的时候，需要先在一块的单元，用（）包起来。如：$res = $house && ($car == 'BMW')
</span><span>268</span><span>//这样可以 使程序易读，易理解 ，不容易产生歧义 </span><span>269</span><span>if</span>(<span>$res</span> = <span>$house</span> && <span>$car</span> == 'BMW'<span>){
</span><span>270</span><span>echo</span> '还是可以嫁'<span>;
</span><span>271</span> }<span>else</span><span>{
</span><span>272</span><span>echo</span> '再等两年'<span>;
</span><span>273</span><span>}
</span><span>274</span><span>275</span><span>逻辑运算的优先级
</span><span>276</span> && 的优先级 比 ||<span>高
</span><span>277</span><span>但是在开发中，不推荐写在一起，应用（）包起来
</span><span>278</span><span>$a</span> = 3<span>;
</span><span>279</span><span>$b</span> = 5<span>;
</span><span>280</span><span>if</span>((<span>$a</span>==8)||(<span>$b</span>=9<span>)){
</span><span>281</span><span>$a</span>++<span>;
</span><span>282</span><span>$b</span>++<span>;
</span><span>283</span><span>}
</span><span>284</span><span>echo</span><span>$a</span>,'<br />',<span>$b</span><span>;
</span><span>285</span><span>286</span><span>//</span><span>==========================================
</span><span>287</span><span>288</span><span>//逻辑反
</span><span>289</span><span>//一个命题如果是真命题，则其反命题，是假命题
</span><span>290</span><span>//用!表示 </span><span>291</span><span>292</span><span>//==========================================
</span><span>293</span><span>//异或运算 xor 返回原处
</span><span>294</span><span>//异或是指，两个条件必须‘一个真’，‘一个假’，才为真</span><span>295</span><span>296</span><span>$li</span> = '男'<span>;
</span><span>297</span><span>$mei</span> = '女'<span>;
</span><span>298</span><span>//</span><span>这个异或表达的是，必须一个为男，</span><span>299</span><span>if</span>(<span>$li</span> == '男') xor (<span>$mei</span> == '男'<span>){
</span><span>300</span><span>echo</span> '可以结婚'<span>;
</span><span>301</span> }<span>else</span><span>{
</span><span>302</span><span>echo</span> '法律禁止，请去北欧'<span>;
</span><span>303</span><span>}
</span><span>304</span><span>305</span><span>306</span><span>//</span><span>==========================================
</span><span>307</span><span>//三元运算符 返回原处
</span><span>308</span><span>//
</span><span>309</span><span>//条件？返回值1：返回值2
</span><span>310</span><span>//如果条件为真，则返回值1，否则返回值2
</span><span>311</span><span>//
</span><span>312</span><span>//
</span><span>313</span><span>//比如，在网站中判断一个人有没有登陆
</span><span>314</span><span>//如果登陆，用户名不为空，则显示其用户名
</span><span>315</span><span>//如果没登陆，用户名空，则显示游客。。
</span><span>316</span><span>317</span><span>//$user = 'zhangsan';
</span><span>318</span><span>//if(!=''){
</span><span>319</span><span>// echo $user;
</span><span>320</span><span>//}else{
</span><span>321</span><span>// echo '游客';
</span><span>322</span><span>//}
</span><span>323</span><span>//
</span><span>324</span><span>//$user = 'zhangsan';
</span><span>325</span><span>//echo $user?$user:'游客';
</span><span>326</span><span>327</span><span>//程序如果没有三元运算符，可以用什么代替？
</span><span>328</span><span>//
</span><span>329</span><span>//可以用if/else代替
</span><span>330</span><span>//三元中是一个简化的写法
</span><span>331</span><span>//而且效率没有 if/esle高
</span><span>332</span><span>333</span><span>334</span><span>//==========================================
</span><span>335</span><span>//递增，递减运算符 返回原处
</span><span>336</span><span>//
</span><span>337</span><span>//就是语言中没有递增，递减，也不会影响我们写程序。
</span><span>338</span><span>//也是一些场景的简化写法
</span><span>339</span><span>340</span><span>//分析，$b + 1是一个算术运算，算出的结果是3，这个3是一个‘算出结果’，和$b没有关系
</span><span>341</span><span>//这个算出结果，值给了$a
</span><span>342</span><span>//因此，$a为3，$b为2</span><span>343</span><span>$b</span> = 2<span>;
</span><span>344</span><span>$a</span> = <span>$b</span> +1<span>;
</span><span>345</span><span>echo</span><span>$a</span>,'~',<span>$b</span>,'<br />'<span>;
</span><span>346</span><span>347</span><span>//</span><span>$b++,这是一个递增运算，去处则必有去处结果，
</span><span>348</span><span>//问题： $b++的运算结果是什么？
</span><span>349</span><span>//答：$b++,运算结果是$b本身
</span><span>350</span><span>//然后再把$b的值+1
</span><span>351</span><span>//就相当于return $b； $b = $b +1;
</span><span>352</span><span>//$b =1;
</span><span>353</span><span>//$a = $b++;
</span><span>354</span><span>//echo $a,'<br />',$b;
</span><span>355</span><span>//
</span><span>356</span><span>//
</span><span>357</span><span>//==========================================</span><span>358</span><span>/*</span><span>位运算符，说白了，就是，二进制运算符 返回原处
</span><span>359</span><span>//人有10个指头，用10进位，便于计算
</span><span>360</span><span>//
</span><span>361</span><span>//玛雅人，不穿鞋，连脚趾也算上，20进位
</span><span>362</span><span>//进位是多少没关系，关键是方便我们我们使用
</span><span>363</span><span>//
</span><span>364</span><span>//对于计算机来说，所有的位，都 只有两种状态 0 1
</span><span>365</span><span>//因为百进位上 ，1代表100
</span><span>366</span><span>//10进位上，1代表10
</span><span>367</span><span>//个位，1代表1
</span><span>368</span><span>//
</span><span>369</span><span>//我们知道计算机里的信息，都是以0，1来存储的
</span><span>370</span><span>//一个可以存储0/1单元，称为位bit
</span><span>371</span><span>//
</span><span>372</span><span>//8个位组成一个字节，Byte
</span><span>373</span><span>//字节是计算机里最基本的单位。
</span><span>374</span><span>375</span><span>376</span><span>12 = 8 + 4；
</span><span>377</span><span> =1*2^3+1*2^2+0*2^1+0*2^0
</span><span>378</span><span> =1100
</span><span>379</span><span>5=101
</span><span>380</span><span>但是计算机里，最基本的单位就是字节，有8个位，只用了3个怎么办？
</span><span>381</span><span>答：把用的3个或4个位，写在字节的右边
</span><span>382</span><span>左边的这些位，用0补上。
</span><span>383</span><span>因此，计算机里：
</span><span>384</span><span>12=0000 1100
</span><span>385</span><span>5 =0000 0101
</span><span>386</span><span>387</span><span>388</span><span>12 & 5 = 0000 0100 = 4
</span><span>389</span><span>12 | 5 = 0000 1101 = 13
</span><span>390</span><span>12 ^ 5 = 0000 1001 =9
</span><span>391</span><span>按位运算符
</span><span>392</span><span>&按位且 ，把2个二进制值齐，把1看成true ，把0看成false，然后每个位上都做 并且 的运算。
</span><span>393</span><span>|按位或 ， 把2个二进制值齐，把1看成true ，把0看成false，然后每个位上都做 或者 的运算。
</span><span>394</span><span>395</span><span>^按位异或 把2个二进制值齐，把1看成true ，把0看成false，然后每个位都不一样时做 异或 的运算。
</span><span>396</span><span>397</span><span>398</span><span>提醒大家：计算机是按位算，我们操作，往往直接10进制
</span><span>399</span><span>*/</span><span>400</span><span>//</span><span>==========================================</span><span>401</span><span>402</span><span>$a</span> = 12<span>;
</span><span>403</span><span>$a</span> = 0000 1100
<span>404</span><span>//</span><span>按位求反</span><span>405</span><span>$a</span> = 1111 0011
<span>406</span><span>echo</span> ~12
<span>407</span><span>//</span><span>计算机里表示负数，是用补码的规则来计算的
</span><span>408</span><span>//具体这样来计算负数，假设有8位
</span><span>409</span><span>//最高位是1，得出符号是负
</span><span>410</span><span>//
</span><span>411</span><span>//开始补码规则
</span><span>412</span><span>//计算除符号位之外，其他7位的绝对值
</span><span>413</span><span>//(1)111 0011 =115
</span><span>414</span><span>//然后把 绝对值-2^7 = 115 -128 = -13
</span><span>415</span><span>//
</span><span>416</span><span>//因此：
</span><span>417</span><span>//1000 0001 ---不要想当然是 -1
</span><span>418</span><span>//而是 1-2^7 = -127</span><span>419</span> 1111 1111 --- 127-128 = -1
<span>420</span> 1000 0000 --- 0-128 =-128
<span>421</span><span>422</span> 0000 0000 --- 0
<span>423</span> 0111 1111 --- 127
<span>424</span><span>425</span><span>//</span><span>为什么有人问：-128 +127
</span><span>426</span><span>//
</span><span>427</span><span>//直观来理解
</span><span>428</span><span>//-128 --- 0 0 --- 127
</span><span>429</span><span>//位运算，掌握更好，掌握的不熟悉也不要纠结
</span><span>430</span><span>431</span><span>432</span><span>//==========================================
</span><span>433</span><span>//移位运算 返回原处</span><span>434</span><span>435</span> 5 = 0000 0101<span>;
</span><span>436</span> 5 << 1; <span>//</span><span>左移
</span><span>437</span><span>//相当于乘2的效果</span><span>438</span> 0000 1010; <span>//</span><span>得到的结果是10 </span><span>439</span> 5 >> 1; <span>//</span><span>右移</span><span>440</span> 0000 0010
<span>441</span><span>//</span><span>相当于除2的效果
</span><span>442</span><span>443</span><span>444</span><span>//==========================================
</span><span>445</span><span>//之前学习了‘量’---变量，常量
</span><span>446</span><span>//量与量之间，可以运算，运算符
</span><span>447</span><span>//
</span><span>448</span><span>//如果只有量与量与的运算，那么我们学的知识只够做一个计算器
</span><span>449</span><span>450</span><span>//==========================================
</span><span>451</span><span>//想写程序：还得有控制结构
</span><span>452</span><span>//
</span><span>453</span><span>//控制结构，就是条件与逻辑，控制代码的执行顺序
</span><span>454</span><span>//
</span><span>455</span><span>//程序员 是用php --- 培训 --- 计算机
</span><span>456</span><span>//如果 --- if
</span><span>457</span><span>//否则如果 ---else if
</span><span>458</span><span>//否则 ---- else </span><span>459</span><span>$gender</span> = <span>$_GET</span>['gender'<span>];
</span><span>460</span><span>if</span><span>(){
</span><span>461</span> }<span>else</span><span>{
</span><span>462</span><span>463</span><span>}
</span><span>464</span><span>//</span><span>==========================================
</span><span>465</span><span>466</span><span>//有几种控制结构
</span><span>467</span><span>//答 : 1. 顺序 、 2. 分支 、 3. 循环
</span><span>468</span><span>//这个3种控制结构
</span><span>469</span><span>//所有语言都这样 返回原处
</span><span>470</span><span>471</span><span>//==========================================
</span><span>472</span><span>// 1. 顺序
</span><span>473</span><span>// 顺序结构就是语句按照你书写的顺序，从前到后顺序执行。
</span><span>474</span><span>// 最容易理解 </span><span>475</span><span>echo</span> 'a:8点了','<br />'<span>;
</span><span>476</span><span>echo</span> 'b:来YY:88354001','<br />'<span>;
</span><span>477</span><span>echo</span> 'c:我听懂了','<br />'<span>;
</span><span>478</span><span>echo</span> 'd:我开始写博客了','<br />'<span>;
</span><span>479</span><span>480</span><span>//</span><span>==========================================
</span><span>481</span><span>// 2. 分支 <span>返回原处</span></span><span>482</span><span>//顾名思义：有分支 ，就像一条大路，走了3岔口，该选择一个走下去了。
</span><span>483</span><span>//最简单的，单路分支
</span><span>484</span><span>485</span><span>//单路分支 </span><span>486</span><span>$age</span> = 18<span>;
</span><span>487</span><span>if</span>(<span>$age</span> >= 18<span> ){
</span><span>488</span><span>echo</span> '你已成年'<span>;
</span><span>489</span> }<span>//</span><span>这个if中的代码，要么执行，要么不执行
</span><span>490</span><span>//括号中的表达式，如果为真，则执行，否则，不执行</span><span>491</span> -------------------------------------------
<span>492</span><span>//</span><span>双路分支 if /else </span><span>493</span><span>$year</span> = 2012<span>;
</span><span>494</span><span>$birth</span> = 1987<span>;
</span><span>495</span><span>$age</span> = <span>$year</span> - <span>$birth</span><span>496</span><span>if</span>(<span>$age</span> > 28<span>){
</span><span>497</span><span>echo</span> '你是中老年'<span>;
</span><span>498</span> }<span>else</span><span>{
</span><span>499</span><span>echo</span> '你是有为青年'<span>;
</span><span>500</span><span>}
</span><span>501</span><span>//</span><span>if为真，则代码段1执行
</span><span>502</span><span>//if为假，则代码段2执行
</span><span>503</span><span>//if else 中的两个代码，有且只有一个执行。
</span><span>504</span><span>//-------------------------------------------
</span><span>505</span><span>//多路分支 </span><span>506</span><span>$age</span> = 34<span>;
</span><span>507</span><span>if</span>( <span>$age</span> <=16<span> ){
</span><span>508</span><span>echo</span> '中年'<span>;
</span><span>509</span> } <span>else</span><span>if</span>(<span>$age</span> > 16 && <span>$age</span> <= 28<span>){
</span><span>510</span><span>echo</span> '老年'<span>;
</span><span>511</span> }<span>else</span><span>if</span>( <span>$age</span> >28 && <span>$age</span> <=300<span>){
</span><span>512</span><span>echo</span> '其他'<span>;
</span><span>513</span><span>}
</span><span>514</span> -------------------------------------------
<span>515</span><span>//</span><span>switch 分支语句 <span>返回原处</span></span><span>516</span><span>517</span><span>$day</span> = 2<span>;
</span><span>518</span><span>if</span>(<span>$day</span> == 1<span>){
</span><span>519</span><span>echo</span> '星期一'<span>;
</span><span>520</span> }<span>else</span><span>if</span>(<span>$day</span> == 2<span>){
</span><span>521</span><span>echo</span> '星期二'<span>;
</span><span>522</span> }<span>else</span><span>if</span>(<span>$day</span> == 3<span>){
</span><span>523</span><span>echo</span> '星期三'<span>;
</span><span>524</span> }<span>else</span><span>if</span>(<span>$day</span> == 4<span>){
</span><span>525</span><span>echo</span> '星期四'<span>;
</span><span>526</span> }<span>else</span><span>if</span>(<span>$day</span> == 5<span>){
</span><span>527</span><span>echo</span> '星期五'<span>;
</span><span>528</span> }<span>else</span><span>if</span>(<span>$day</span> == 6<span>){
</span><span>529</span><span>echo</span> '星期六'<span>;
</span><span>530</span> }<span>else</span><span>if</span>(<span>$day</span> == 7<span>){
</span><span>531</span><span>echo</span> '星期日'<span>;
</span><span>532</span> }<span>else</span><span>{
</span><span>533</span><span>echo</span> '不存在'<span>;
</span><span>534</span><span>}
</span><span>535</span><span>//</span><span>对于一个变量的值，有多种可能性，用if / if else 来比较，当然是可以的。
</span><span>536</span><span>//但是，有一种，更简单的分支结构来替换他</span><span>537</span><span>538</span><span>539</span><span>$day</span> =2<span>;
</span><span>540</span><span>switch</span>(<span>$day</span><span>){
</span><span>541</span><span>case</span> 1:
<span>542</span><span>echo</span> '星期一'<span>;
</span><span>543</span><span>break</span><span>;
</span><span>544</span><span>case</span> 2:
<span>545</span><span>echo</span> '星期二'<span>;
</span><span>546</span><span>break</span><span>;
</span><span>547</span><span>case</span> 3:
<span>548</span><span>echo</span> '星期三'<span>;
</span><span>549</span><span>break</span><span>;
</span><span>550</span><span>case</span> 4:
<span>551</span><span>echo</span> '星期四'<span>;
</span><span>552</span><span>break</span><span>;
</span><span>553</span><span>case</span> 5:
<span>554</span><span>echo</span> '星期五'<span>;
</span><span>555</span><span>break</span><span>;
</span><span>556</span><span>case</span> 6:
<span>557</span><span>echo</span> '星期六'<span>;
</span><span>558</span><span>break</span><span>;
</span><span>559</span><span>case</span> 7:
<span>560</span><span>echo</span> '星期日'<span>;
</span><span>561</span><span>break</span><span>;
</span><span>562</span><span>default</span>:
<span>563</span><span>echo</span> '其他'<span>;
</span><span>564</span> }<span>//</span><span>从上到下，判断$day和case指定的值，是否相等，如果相等，就执行以后的语句，否则就不执行。
</span><span>565</span><span>//因此，一定要用break退出
</span><span>566</span><span>//如果没用switch case的话我们可以用什么替换？
</span><span>567</span><span>//
</span><span>568</span><span>//答：if / else if else 来替换 ，
</span><span>569</span><span>//
</span><span>570</span><span>//问：switch case ,与，if/esle if/else 相比，各适合什么 样的场合？
</span><span>571</span><span>//switch case 只能判断某变量是否与指定的值相等
</span><span>572</span><span>//
</span><span>573</span><span>//比如：值 1，2，3，4……
</span><span>574</span><span>//但是不能用来判断范围
</span><span>575</span><span>//
</span><span>576</span><span>//而if/ else if /else 可用来判断 范围，甚至更复杂的判断表达式，也可以
</span><span>577</span><span>//而case ，却只能提供一个准备的值，和变量做相等的比较。
</span><span>578</span><span>//如果 需要和几个确认的值比较是否相等，适合用switch\
</span><span>579</span><span>580</span><span>//==========================================
</span><span>581</span><span>582</span><span>//循环结构
</span><span>583</span><span>//编程语言，一般都有for , while , do /while 循环
</span><span>584</span><span>//
</span><span>585</span><span>//先看while <span><span>返回原处</span></span></span><span>586</span><span>//while(表达式){
</span><span>587</span><span>// 语句;
</span><span>588</span><span>//}
</span><span>589</span><span>//判断表达式是否为真，如果为真，则执行语句
</span><span>590</span><span>//执行完语句之后，再回到while 开始处，判断表达式是否为真
</span><span>591</span><span>//如果为真……
</span><span>592</span><span>//…………
</span><span>593</span><span>//……
</span><span>594</span><span>//如果假，本次循环结束 </span><span>595</span><span>596</span><span>$hard</span> = 100<span>;
</span><span>597</span><span>$hit</span> = -1<span>;
</span><span>598</span><span>599</span><span>while</span>(<span>$hard</span> >= 30<span>){
</span><span>600</span><span>$hard</span> = <span>$hard</span> + <span>$hit</span><span>;
</span><span>601</span><span>if</span>(<span>$hard</span> >=30<span>){
</span><span>602</span><span>echo</span> '不服','<br />'<span>;
</span><span>603</span> }<span>else</span><span>{
</span><span>604</span><span>echo</span> '服了','<br />'<span>;
</span><span>605</span><span> }
</span><span>606</span><span>}
</span><span>607</span><span>echo</span><span>$hard</span>,'服了吧'<span>;
</span><span>608</span> -------------------------------------------
<span>609</span><span>while</span><span>(){
</span><span>610</span> }<span>//</span><span> 也有一次都不执行的，第一次条件就不成立，直接退出。</span><span>611</span><span>$hard</span> = 20<span>;
</span><span>612</span><span>$hit</span> = -1<span>;
</span><span>613</span><span>614</span><span>while</span>(<span>$hard</span> >= 30<span>){
</span><span>615</span><span>$hard</span> = <span>$hard</span> + <span>$hit</span><span>;
</span><span>616</span><span>if</span>(<span>$hard</span> >=30<span>){
</span><span>617</span><span>echo</span> '不服','<br />'<span>;
</span><span>618</span> }<span>else</span><span>{
</span><span>619</span><span>echo</span> '服了','<br />'<span>;
</span><span>620</span><span> }
</span><span>621</span><span>}
</span><span>622</span><span>623</span><span>//</span><span>-------------------------------------------
</span><span>624</span><span>//
</span><span>625</span><span>//如果碰到下面的情况</span><span>626</span><span>while</span>(<span>true</span><span>){
</span><span>627</span><span>echo</span> 'haha<br />'<span>;
</span><span>628</span> }<span>//</span><span>死循环</span><span>629</span> -------------------------------------------
<span>630</span><span>do</span><span>{ <span><span><span>返回原处</span></span></span></span><span>631</span><span>632</span> }<span>while</span><span>();
</span><span>633</span><span>//</span><span>do ，即执行，上来先执行一下语句，然后再去判断
</span><span>634</span><span>//所有，do/while 到至少执行一次</span><span>635</span><span>636</span><span>$hard</span> = 20<span>;
</span><span>637</span><span>$hit</span> = -1<span>;
</span><span>638</span><span>do</span><span>{
</span><span>639</span><span>$hard</span> = <span>$hard</span> + <span>$hit</span><span>;
</span><span>640</span><span>if</span>(<span>$hard</span> >=30<span>){
</span><span>641</span><span>echo</span> '不服','<br />'<span>;
</span><span>642</span> }<span>else</span><span>{
</span><span>643</span><span>echo</span> '服了','<br />'<span>;
</span><span>644</span><span> }
</span><span>645</span> }<span>while</span>(<span>$hard</span>>=30<span>);
</span><span>646</span><span>647</span><span>//</span><span>==========================================
</span><span>648</span><span>//for(语句1;语句2;语句3){ <span><span><span>返回原处</span></span></span></span><span>649</span><span>// 代码段;
</span><span>650</span><span>//}
</span><span>651</span><span>//语句1，先执行 且只执行1次
</span><span>652</span><span>//然后 语句2判断，如为真，则执行 代码段; ，然后执行 语句3;
</span><span>653</span><span>//
</span><span>654</span><span>//再语句2判断……循环
</span><span>655</span><span>//直到语句2为假，for结束
</span><span>656</span><span>//
</span><span>657</span><span>//-------------------------------------------------------
</span><span>658</span><span>//打印1到100的整数，如果是3的倍数就打印Fizz,如果是5的倍数就打印Buzz
</span><span>659</span><span>//如果是3和5的倍数就打印abcd</span><span>660</span><span>$i</span> = 0<span>;
</span><span>661</span><span>while</span>(++<span>$i</span><=100<span>){
</span><span>662</span><span>if</span>(<span>$i</span>%15 == 0<span>){
</span><span>663</span><span>echo</span><span>$i</span>,'----abcd----即是3的倍数，又是5的倍数','<br />'<span>;
</span><span>664</span> }<span>else</span><span>if</span>(<span>$i</span>%3 == 0<span>){
</span><span>665</span><span>echo</span><span>$i</span>,'----FiZZ----3的倍数','<br />'<span>;
</span><span>666</span> }<span>else</span><span>if</span>(<span>$i</span>%5 == 0<span>){
</span><span>667</span><span>echo</span><span>$i</span>,'----BuZZ----5的倍数','<br />'<span>;
</span><span>668</span> }<span>else</span><span>{
</span><span>669</span><span>echo</span><span>$i</span>,'<br />'<span>;
</span><span>670</span><span> }
</span><span>671</span><span>}
</span><span>672</span> -------------------------------------------------------
<span>673</span><span>674</span><span>//</span><span>公鸡 5元1只，小鸡1元3只，母鸡 3元1只
</span><span>675</span><span>//100元买回100只，问公鸡，母鸡，小鸡各多少只？</span><span>676</span><span>for</span> (<span>$g</span> = 1;<span>$g</span><=20;<span>$g</span>++<span>){
</span><span>677</span><span>for</span>(<span>$m</span> = 1;<span>$m</span><=34;<span>$m</span>++<span>){
</span><span>678</span><span>$x</span> = 100-<span>$g</span>-<span>$m</span><span>;
</span><span>679</span><span>if</span>(5*<span>$g</span>+3*<span>$m</span>+<span>$x</span>/3 == 100<span>){
</span><span>680</span><span>echo</span> '公鸡',<span>$g</span>,'只，','母鸡',<span>$m</span>,'只，','小鸡，',<span>$x</span>,'只,<br />'<span>;
</span><span>681</span><span> }
</span><span>682</span><span> }
</span><span>683</span><span>}
</span><span>684</span><span>//</span><span>==========================================
</span><span>685</span><span>//
</span><span>686</span><span>//break 有破坏的意思，直接破坏整个循环语句，不再往下执行了。</span><span>687</span><span>688</span><span>for</span>(<span>$i</span> = 1;<span>$i</span> < 10;<span>$i</span>++<span>){
</span><span>689</span><span>if</span>(<span>$i</span> == 6<span>){
</span><span>690</span><span>break</span><span>;
</span><span>691</span> }<span>else</span><span>{
</span><span>692</span><span>echo</span><span>$i</span>,'<br />'<span>;
</span><span>693</span><span> }
</span><span>694</span><span>}
</span><span>695</span> --------------------------------------------------------
<span>696</span><span>//</span><span>continue 有继续的意思，跳出本次循环，继续执行下一次循环</span><span>697</span><span>for</span>(<span>$i</span> = 1;<span>$i</span> < 10;<span>$i</span>++<span>){
</span><span>698</span><span>if</span>(<span>$i</span> == 6<span>){
</span><span>699</span><span>continue</span><span>;
</span><span>700</span> }<span>else</span><span>{
</span><span>701</span><span>echo</span><span>$i</span>,'<br />'<span>;
</span><span>702</span><span> }
</span><span>703</span><span>}
</span><span>704</span><span>705</span> --------------------------------------------------------
<span>706</span><span>//</span><span>过收费站，手上有钱100，000元，当钱>50000时，交手上钱数的5%元，当钱数<=50，000时，每次交5000元，问能过几次？</span><span>707</span><span>for</span>(<span>$i</span>=0,<span>$money</span> = 100000;<span>$money</span> >= 5000;){ <span>//</span><span>看此处，第2个‘;’号后竟然是空//的</span><span>708</span><span>if</span>(<span>$money</span>>50000<span>){
</span><span>709</span><span>$money</span> *= 0.95<span>;
</span><span>710</span> }<span>else</span><span> {
</span><span>711</span><span>$money</span> -= 5000<span>;
</span><span>712</span><span>713</span><span> }
</span><span>714</span><span>$i</span>+=1<span>;
</span><span>715</span><span>echo</span> '第', <span>$i</span>,'过桥后','剩下的钱数为',<span>$money</span>,'<br />'<span>;
</span><span>716</span><span>}
</span><span>717</span><span>718</span><span>719</span><span>//</span><span>如下</span><span>720</span><span>for</span><span>(){
</span><span>721</span><span>echo</span> 'haha'<span>;
</span><span>722</span><span>//</span><span>别运行，死循环</span><span>723</span><span>}
</span><span>724</span><span>725</span><span>726</span> */<br>相关的视频连接:<br>1. 位运算符 ,移位运算<br>2.三大控制结构之顺序和分支</span>
The above introduces the Java operators, operators and control structures in PHP, including the content of Java operators. I hope it will be helpful to friends who are interested in PHP tutorials.
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