C++谭浩强 课后习题 第四章函数预处理 4

#include <iostream>
using namespace std;
int fac(int);
int main()
{
 int a,b,c;
 cout<<"please enter a,b,c";
 cin>>a>>b>>c;
 cout<<"a!="<<fac(a)<<","<<"b!="<<fac(b)<<","<<"c!="<<fac(c)<<endl;
 system("pause");
 return 0;
}
int fac(int x)
{
 int y;
if (x<0)
{
 cout<<"error!"<<endl;
 y=-1;
}
else if(x==0 || x==1)y=1;
else y=fac(x-1)*x;
 return y;
}