#include <iostream>
using namespace std;

// 变量声明
extern int a, b;
extern int c;
extern float f;
  
int main ()
{
    // 变量定义
    int a, b;
    int c;
    float f;
 
    // 实际初始化
    a = 10;
    b = 20;
    c = a + b;
 
    cout << c << endl ;
    f = 70.0/3.0;
    cout << f << endl ;
    return 0;
}