Learn point C language (34): function

1. Local Variables:

A local variable is also called an automatic variable, which declares that at the beginning of a function, it lives on the stack, and its life ends with the function returning.

#include　<stdio.h>

int　main(void)
{
　　auto　int　i　=　9;　/*　声明局部变量的关键字是auto;因可以省略,几乎没人使用　*/

　　printf("%d\n",i);
　　getchar();
　　return　0;
}

2. Global variables:

The global variable declaration is outside the function body and should be in front of the function. Every function can use it, but global variables should be used sparingly.

#include　<stdio.h>

void　add(void);
void　mul(void);

int　gi　=　3;　/*　全局变量　*/

int　main(void)
{
　　printf("%d\n",gi);　/*　3　*/

　　add();
　　printf("%d\n",gi);　/*　5　*/

　　mul();
　　printf("%d\n",gi);　/*　10　*/

　　getchar();
　　return　0;
}

void　add(void)　{
　　gi　+=　2;
}

void　mul(void)　{
　　gi　*=　2;
}

The global variable is initialized to null, and the local variable is a garbage value before it is assigned:

#include　<stdio.h>

int　gi;　/*　全局变量　*/

int　main(void)
{
　　int　i;　/*　句柄变量　*/

　　printf("%d,%d\n",gi,i);

　　getchar();
　　return　0;
}

When a global variable has the same name as a local variable, a local variable is used:

#include　<stdio.h>

int　a　=　111,b　=　222;

int　main(void)
{
　　int　a　=　123;
　　printf("%d,%d\n",a,b);　/*　123,222*/

　　getchar();
　　return　0;
}