1、 C language program structure, compilation and operation, data type related

1、C Language program structure

• Preprocessing instruction ： Tell the calculator before the official compilation , To include the corresponding header file
• The main function ：int main() Where the program starts
• Return value :return 0; At the end of the program , The result returned , The same type as the main function

// 1. Preprocessing instruction , Tell the calculator before the official compilation , To include the corresponding header file 
#include<stdio.h>

// 2. Where the program starts 
int main(){
    
    printf("hello world!\n");
    return 0;// After the function terminates , return 0
}

2、 Compiling and running process

• compile ：
  • Format ：gcc Source file .c -o Object file's .out
  • Be careful ： Multiple files can be compiled at the same time gcc test1.c test2.c -o main.out
  • Specify the location where the target file is generated gcc test1.c -o Target file /main.out
  • -o The two documents before and after are interchangeable , The effect is the same gcc -o main.out test1.c
  • Be careful ： stay Windows in , The suffix of the target file is .exe
• perform ：
  • command ：./main.out

3、 Data type related

1. View data store size

• Code implementation ：

  #include<stdio.h>
  int main(){
        
      printf(" Storage size ：%ld byte \n",sizeof(double));
      return 0;
  }
  

• Running results ：

   Storage size ：8 byte 
  

2.float.h Related macro definitions

• stay float.h Header file , Defines related macros
• Code implementation ：

  #include<stdio.h>
  #include<float.h>
  int main(){
        
      printf("float Store the maximum number of bytes ：%lu\n",sizeof(float));
      printf("float minimum value ：%E\n",FLT_MIN);
      printf("float Maximum ：%E\n",FLT_MAX);
      printf(" double-precision value ：%d\n",FLT_DIG);
      return 0;
  }
  

• Running results ：

  float Store the maximum number of bytes ：4
  float minimum value ：1.175494E-38
  float Maximum ：3.402823E+38
   double-precision value ：6
  

3. Data type conversion

3.1 Automatic conversion

• Assign floating point numbers to integers , The decimal value will be automatically removed
• Integer assigned to floating point number , The value remains the same , But it will be stored in floating-point variables

3.2 Coercive transformation

• Format ：( Type specifier )( expression )
• Code implementation ：

  #include<stdio.h>
  int main(){
        
      float f,x = 2.3, y = 4.3;
      int i = 4,a,b;
      a = x + y;// The decimal part will be removed 
      b = (int)(x + y);
      f = 10/i;// Divide two shapes , The result is still plastic , The result is 2, then 2 Stored in floating point type 
      printf("a=%d,b=%d,f=%f",a,b,f);
      return 0;
  }
  

• Running results ：

  a=6,b=6,f=2.000000