C language learning log 1.2

One . Pointer use cases ：

(1): Function returns multiple variables , for example :

#include<stdio.h>
void minmax(int a[], int len, int *max,int *min);
int main(void){
    int a[] ={1,2,3,4,5,6,7,8,9,10,14,16,17,21,23,66};
    int min,max;
    minmax(a,sizof(a)/sizof(a[0]),&min,&max);
    return 0;
}
void minmax(int a[], int len, int *min, int *max)
{
    int i;
    *min =*max =a[0];
    for(i=1;i<len;i++){
        if(a[i] <*min) *min = a[i];
        if(a[i] >*max) *max= a[i];
    }
}

(2) Function returns the operation status , The result returns... Through the pointer , for example ：

#include<stdio.h>
int divide(int a,int b,int *result);
int main(void)
{
	int a=5,b=2,c;
	if(divide(a,b,&c){
		printf("%d / %d = %d",a,b,c);
	}
	return 0;
}
int divide(int a,int b,int *result);
{
	int ret=1;
	if(b==0){
		ret=0;
	}else{
		*result=a/b;
	}
	return ret;
}

Two . About adding... To a pointer const

Pointer is const: Indicates that once the address of a variable is obtained , Cannot point to other variables .

for example :int *const q=&i;  q yes const

Refers to const： Indicates that the variable cannot be modified through this pointer ( It can't be that variable that becomes const)

for example :const int *p =&i; *p Assignment operation is not allowed .

The way of distinction : Judge const stay * Front or back , In the front, it means const, After that, the pointer is const.

Tips：const int a[]={1,2,3,4,5} It means const Array , The array itself is a const The pointer represents a This array cannot point to other arrays , Add another one outside const It means that the value in it cannot be changed , So this kind of array can only be assigned by initialization .