Detailed explanation of the usage of C++ Boolean types and references

1. Boolean type

The Boolean type in C

• C adds bool# on top of the basic type system of C language.

• ##The only possible values ​​for

  bool in C are true and false

• Theoretically

  bool occupies one byte

Note:

true represents the true value, The compiler internally uses 1 to represent

false represents a non-true value, and the compiler internally uses 0 to represent

In C language:

is represented by an integer Type value replaces the

bool type, commonly used 0:flase, 1:true

##C has made type enhancements and added a very rigorous

bool

type, true and false exist as keywords. In the Boolean type of C, the

bool

type only has two values: true and false. The C compiler will convert non-0 values is true, a value of 0 is converted to false. <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:css;toolbar:false;">bool b = 0; printf(&quot;b = %d\n&quot;, b); b++; printf(&quot;b = %d\n&quot;, b); b = b - 3; printf(&quot;b = %d\n&quot;, b); // bool类型是否支持数学运算？</pre><div class="contentsignin">Copy after login</div></div>In fact, in C language, the internal implementation of the Boolean type is implemented as a byte integer. The

bool

type supports mathematical operations, and the compiler will make adjustments internally. Non-0 is true, 0 is falseCode test:

#include <stdio.h>

int main(int argc, char *argv[])
{
    bool b = false;
    int a = b;
    
    printf("sizeof(b) = %d\n", sizeof(b));
    // sizeof(b) = 1, bool类型占一个字节
    printf("b = %d, a = %d\n", b, a);    0
    // b = 0, a = 0
    
    b = 3;    // b = 1
    a = b;  // a = 1
    
    printf("b = %d, a = %d\n", b, a);
    
    b = -5;    // b = 1
    a = b;  // a = 1
    
    printf("b = %d, a = %d\n", b, a);
    
    a = 10; // a = 10
    b = a;  // b = 1
    
    printf("a = %d, b = %d\n", a, b);
    
    a = 0;    // a = 0
    b = a;  // b = 0
    
    printf("a = %d, b = %d\n", a, b);
    
    return 0;
}

Boolean type is the basic data type in C

can be defined Global variables of type
• bool

can be defined# Constants of type
• bool

can be defined# A pointer of type ##bool

• can define an array of type
bool

• ......

2. Ternary operator

The ternary operator has been upgraded in C

Consider whether the following code is correct, respectively in C language and C Compile and run the test in the environment

int a = 1;
int b =2;
(a < b ? a : b) = 3;
printf("a = %d, b = %d\n", a, b);
// 在C语言中报错
// 在C++中，结果a = 3

Ternary operator

The ternary operator in C language returns the variable value

cannot be used as an lvalue

#The ternary operator in C can directly return the variable itself
Can be used as both an rvalue and an lvalue

Note:

Possible values ​​returned by the ternary operator If one of them is a constant value, it cannot be used as an lvalue.

The ternary operator can only be used as an lvalue when all possible returns are variables. A constant and a variable cannot be used as an lvalue. What is the significance of such an upgrade to the ternary operator using

C?

When all possible returns of the ternary operator are variables,

returns the variable itself

, which leads to a new concept: Quote

3, Quote

3.1 Variable name

A variable is an alias for an actual continuous storage space. In the program, the storage space is applied for and named through variables. The storage space can be used through the name of the variable.

Question: Can a continuous storage space have only one alias?

3.2 Reference

Reference in C

The concept of reference is added in C

int a = 4;
int& b = a;     // b作为a的别名
b = 5;        // 操作b就是操作a

The reference can be regarded as an alias of a defined variable

• The syntax of the reference:
Type& name = var;
Note:

Ordinary references must be initialized with variables of the same type when they are defined.

What does C do with the ternary operator?

int a = 1;
int b = 2;
(a < b ? a : b) = 3;    // ok，返回a或b的引用，可作为左值
(a < b ? 1 : b) = 4;    // err，返回1或b的值，不能作为左值

When the possible returns of the ternary operator are all variables, what is returned is
variable reference

• When there is a constant in the possible return of the ternary operator, the
value is returned

4. Summary# The ##bool

type is a newly added basic type of C. The values ​​of the

bool type can only be true

and falseThe ternary operator in C can be used as an lvalueReferences in C can be used as aliases of variables

The possible returns of the ternary operator are all variables When, the reference is returned

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