HTML operators, type conversions-HTML Tutorial-php.cn

1.Type conversion:

is divided into automatic conversion and forced conversion, and forced conversion is generally used.

Convert other types to integers: parseInt();

Convert other types to decimals: parseFloat();

Determine whether it is a legal number type: isNaN();

is a number, it returns false, if it is not a number, it returns ture.

Example:

You need to put the prompt

into the isNaN method

2.Operator:

Mathematical operators : + - * / % ++ --；

Relational operator : == ! = >= <= > <;

Logical operators : && || ! ;

Other operators : += -= *= /= %= ? : ;

3.Statement:

are generally divided into sequence, branch and loop statements.

(1) branch statement if:

(judgment condition)

{

Statements to be executed when conditions are met

}

else

{

Statement executed when the condition is not met

}

(2) loop for statement:

for

(initial condition; loop condition; state change)

{

Cycle

}

(3) Problem type: exhaustive, iterative.

(4) Two keywords: break and continue.

(5) If you want to output the value of a certain parameter: the output value is "+a+" and "+b"

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I will disappear.

$("id1") is equivalent to document.getElementById("id1")

Five practice questions

1. Input integers a and b. If a2+b2 is greater than 100, output a2+b2 with hundreds or more digits, otherwise output the sum of the two numbers

<script> function dianji() { var a = parseInt(document.getElementById("a").value); var b = parseInt(document.getElementById("b ").value); if(a*a+b*b>100) { alert(a*a+b*b); } else { alert(a+b); } } </script>

2. Enter a year to determine whether it is a leap year (a year that is evenly divisible by 4 but not 100. A century year that is evenly divisible by 400 is a leap year)

<script> function check() { var a =parseInt (document.getElementById("run").value); if(a%4==0&&a%100!=0 || a%400==0) { alert("You entered a leap year") ; } else { alert("Not a leap year"); } } </script>

3. Standard weight:
Men’s weight=height-100±3
Women’s weight=height-110±3

Please enter gender:

Please enter your height:

Please enter your weight:

<script> function tizhong() { var sex =document.getElementById("sex").value; var height =parseFloat(document.getElementById("height").value); var weight = parseFloat(document.getElementById("weight").value ); if(sex=="male") { var zhong = height-100-weight; if(zhong<=3&&zhong>=-3) { alert("standard weight") } else if(zhong>3) { alert("Underweight, eat more") } else { alert("Overweight, exercise more") } } else if(sex== "Female") { var zhong = height-110-weight; if(zhong<=3&&zhong>=-3) { alert("standard weight") } else if(zhong>3) { alert("Underweight, eat more") } else { alert("Overweight, exercise more") } } else { alert("Incorrect gender input!") } } </script>

4. For a game, the first 20 levels are each level’s own score.
Levels 21-30 are each 10 points.
Levels 31-40 are each 20 points.
Levels 41-49 are each level. 30 points
50 levels is 100 points
//Enter the number of levels you have passed now, and find the score you have now

Please enter the number of levels you have passed now:
<script> function jisuan() { var a = parseInt(document.getElementById("game").value); if(a>0&&a<=50) { var sum=0; for(var i=1;i<=a;i++) { if(i<=20) { sum+=i; } else if(i<=30) { sum+=10; } else if(i<=40) { sum+=20; } else if(i<=49) { sum+=30; } else { sum+=100; } } alert("The total score you obtained is: "+sum) } else { alert("Incorrect input!") } } </script>

5. Enter the ages of 10 people from the console into the array, and sum the ages of the ten people

Please enter the first person in the text box Age: