#include <stdio.h>
 
/* 全局变量声明 */
int a = 20;
 
int main (){
  /* 在主函数中的局部变量声明 */
  int a = 10;
  int b = 20;
  int c = 0;
  int sum(int, int);

  printf ("value of a in main() = %d\n",  a);
  c = sum( a, b);
  printf ("value of c in main() = %d\n",  c);

  return 0;
}

/* 添加两个整数的函数 */
int sum(int a, int b){
    printf ("value of a in sum() = %d\n",  a);
    printf ("value of b in sum() = %d\n",  b);

    return a + b;
}