1 boolean type

• Boolean types in C + +

  • C + + adds bool to the basic type system of C language
  • The only acceptable values of bool in C + + are true and false
  • bool takes only one byte

• be careful:

  • True represents the true value, and the compiler uses 1 internally
  • false represents a non true value, which is internally represented by 0 in the compiler

• Boolean value

  • bool type has only two values: true (non-0) and false (0)
  • The C + + compiler converts non-0 values to true and 0 values to false

• Examples of Boolean types

  • Demo

    #include <stdio.h>
    
    int main(int argc, char *argv[])
    {
        bool b = false;
        int a = b;
        
        printf("sizeof(b) = %d\n", sizeof(b));  //1
        printf("b = %d, a = %d\n", b, a);  //0，0
        
        b = 3;  //b = true;
        a = b;  //a = 1
        
        printf("b = %d, a = %d\n", b, a);  //1，1
        
        b = -5;  //b = true
        a = b;  //a = 1
        
        printf("b = %d, a = %d\n", b, a);  //1，1
        
        a = 10;
        b = a;  //b = false
        
        printf("a = %d, b = %d\n", a, b);  //10，1
        
        a = 0;
        b = a;  //b = false
        
        printf("a = %d, b = %d\n", a, b);  //0，0
        
        return 0;
    }
    

• Boolean type is the basic data type in C + +

  • Global variables of type bool can be defined
  • Constants of type bool can be defined
  • A pointer of type bool can be defined
  • An array of bool types can be defined
  • . . .

2 ternary operator

• C + + upgraded the ternary operator

• Question: is the following code correct?

  int a = 1;
  int b = 2;
  
  (a < b ? a : b) = 3;
  
  printf("a = %d,b = %d\n",a,b);
  

  • C language compiler compilation: error: lvalue required as left operate of assignment
  • C + + compiler compilation: correct: a = 3,b = 2

• The ternary operator in C language returns a variable value and cannot be used as an lvalue

• The ternary operator in C + + can directly return the variable itself, which can be used as both an R-value and an l-value

• Note: if the ternary operator may return a constant value, it cannot be used as an lvalue

3 references

• Variable name

  • A variable is an alias for an actual contiguous storage space
  • The program applies for and names the storage space through variables
  • The storage space can be used by the name of the variable
  

• Question: can only one alias be used for a continuous storage space?

  • There can be multiple = > references

• References in C + +

  • A reference can be seen as an alias for a defined variable

  • Syntax of reference: Type & name = VaR;

    int a  = 4;
    int& b = a;  //b is the alias of a
    
    b = 5;  //Operation b is operation a
    

  • Note: common references must be initialized with variables of the same type when they are defined

• Reference example

  • Demo

    #include <stdio.h>
    
    int main(int argc, char *argv[])
    {
        int a = 4;
        int& b = a;
        
        b = 5;
        
        printf("a = %d\n", a);  //5
        printf("b = %d\n", b);  //5
        printf("&a = %p\n", &a);  //&a = 0xbfe54aec
        printf("&b = %p\n", &b);  //&b = 0xbfe54aec
        
        return 0;
    }
    

• What does C + + do with ternary operators?

  • When all the possible returns of the ternary operator are variables, the variable reference is returned
  • When there is a constant in the possible return of the ternary operator, the value is returned

  int a = 1;
  int b = 2;
  
  (a < b ? a : b) = 3;  //Correct, return the reference of a or b, which can be used as an lvalue
  (a < b ? 1 : b) = 4;  //Error, return the value of 1 or b, which cannot be used as an lvalue