传值和传址：

看下面的代码（传值）：

#include
    
     void swap (int x, int y);void swap (int x, int y){    int t;        printf("In swap,互换前：x = %d, y = %d\n", x, y);//x = 3,y = 5;        t = x;    x = y;    y = t;        printf("In swap,互换后：x = %d, y = %d\n", x, y);//x = 5,y = 3;    }int main (){    int x = 3, y = 5;        printf("In main,互换前：x = %d, y = %d\n", x, y);//x = 3, y = 5;    swap(x, y);    printf("In main,互换后：x = %d, y = %d\n", x, y);//x = 3, y = 5;        return 0; }
    

运用指针之后（传址）：

#include
    
     void swap (int *x, int *y);void swap (int *x, int *y){    int t;        printf("In swap,互换前：x = %d, y = %d\n", *x, *y);//x =  3,y = 5;        t = *x;    *x = *y;    *y = t;    printf("In swap,互换后：x = %d, y = %d\n", *x, *y);//x = 5,y = 3;int main (){    int x = 3, y = 5;        printf("In main,互换前：x = %d, y = %d\n", x, y);//x = 3,y = 5;    swap(&x, &y);//注意这里是交换地址     printf("In main,互换后：x = %d, y = %d\n", x, y);//x = 5, y = 3;        return 0;  }
    

函数无法改变实参的值不懂参考

可变参数

#include
    
     - va list- va start- va arg- va end
    

代码：

#include
    
     #include
     
      有很多宏，可以处理可变参数的函数 int sum (int n,...);//"..."代表占位符，未知数量 ，至少一个 int sum (int n,...){    int i, sum = 0;        va_list vap;//定义参数列表         va_start(vap, n);//初始化参数列表     for(i = 0;i < n;i++)    {        sum += va_arg(vap, int);//获取参数的值 ,参数的类型写清楚     }    va_end(vap);//关闭参数列表         return sum; }int main (){    int r;    r = sum(3, 1, 2, 3);    printf("r = %d\n", r);    return 0;  }