变量声明

#include <stdio.h>

// Variable declaration:
extern int a, b;
extern int c;
extern float f;

int main () {

   /* 变量定义: */
   int a, b;
   int c;
   float f;

   /* 变量初始化 */
   a = 10;
   b = 20;

   c = a + b;
   printf(value of c : %d \n, c);

   f = 70.0/3.0;
   printf(value of f : %f \n, f);

   return 0;
}