问一个关于c++作用域的问题

Question

#include

using namespace std;

void a(int i);

int x=1;

int main()
{
int x=5;
cout<<"local x in outer scope of main is "<<x<<endl;
{
int x=7;
cout<<"local x in inner scope of main is "<<x<<endl;
}
cout<<"local x in outer scope of main is "<<x<<endl;

a(10);  //使用了全局变量 

return 0;

}

void a(int i)
{
cout<<endl<<"global x is "<<x<<" on entering a";
x*=i;
cout<<endl<<"global x is "<<x<<" on entering a";
}

这段代码中“a(10);”为什么调用的是“x=1"这个全局变量？

Answer 1

 void a(int i)
 {
 cout<<endl<<"global x is "<<x<<" on entering a";
 x*=i;
 cout<<endl<<"global x is "<<x<<" on entering a";
 }

请看函数a的定义，里面

 cout<<endl<<"global x is "<<x<<" on entering a";

这句x在函数中是没有申明的，说明x是全局变量，而我们可以看到在main函数之外就定义了全局变量x，并初始化为1了。