定义外部变量

file1.c

include <stdio.h>

int A; /定义外部变量/

void main()
{
int power(int); /函数声明/
int b = 3, c, result, m;

  printf("enter the number A and its power m:\n");
  scanf("%d %d", &A, &m);
  
  c = A * b;
  printf("%d * %d = %d\n", A, b, c);

  result = power(m);
  printf("%d ^ %d = %d\n", A, m, result);

}

---

file2.c

extern A; /声明A为一个已定义的外部变量/

int power(int n)
{
int i, y = 1;

  for(i=1; i <= n; i++)
  {
        y *= A;
  }

  return y;

}