吴裕雄--天生自然C语言开发：作用域规则

#include <stdio.h>
 
int main ()
{
  /* 局部变量声明 */
  int a, b;
  int c;
 
  /* 实际初始化 */
  a = 10;
  b = 20;
  c = a + b;
 
  printf ("value of a = %d, b = %d and c = %d\n", a, b, c);
 
  return 0;
}

#include <stdio.h>
 
/* 全局变量声明 */
int g;
 
int main ()
{
  /* 局部变量声明 */
  int a, b;
 
  /* 实际初始化 */
  a = 10;
  b = 20;
  g = a + b;
 
  printf ("value of a = %d, b = %d and g = %d\n", a, b, g);
 
  return 0;
}

#include <stdio.h>
 
/* 全局变量声明 */
int g = 20;
 
int main ()
{
  /* 局部变量声明 */
  int g = 10;
 
  printf ("value of g = %d\n",  g);
 
  return 0;
}

#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;
}