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 = ;
  b = ;
  c = a + b;

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

  return ;
}

#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 = ;
  b = ;
  g = a + b;

  printf ("value of a = %d, b = %d and g = %d\n", a, b, g);

  return ;
}

#include <stdio.h>

/* 全局变量声明 */
int g = ;

int main ()
{
  /* 局部变量声明 */
  int g = ;

  printf ("value of g = %d\n",  g);

  return ;
}

#include <stdio.h>

/* 全局变量声明 */
int a = ;

int main ()
{
  /* 在主函数中的局部变量声明 */
  int a = ;
  int b = ;
  int c = ;
  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 ;
}

/* 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;
}