#include <iostream>
using namespace std;
int main()
    {
int a;
cout<<"*******************"<<endl;
cout<<" "<<endl;
cout<<"     游戏开始"<<endl;
cout<<"   你考了多少分？"<<endl;
cout<<" (请输入三科总成绩)"<<endl;

cout<<" "<<endl;
cout<<"        ";
cin>>a ;
if(a<=0)
{
cout<<"       错误！"<<endl;
cout<<"*******************";
}
if(a<=0,a<50)
{
cout<<"  "<<endl;
cout<<"   男女混合双打!"<<endl ;
cout<<"     游戏结束！"<<endl;
cout<<" "<<endl;
cout<<"*******************";
}
else if(a<=50,a<100)
{
cout<<" "<<endl;
cout<<"     女子单打!"<<endl;
cout<<"     游戏结束！"<<endl;
cout<<" "<<endl;
cout<<"*******************";
}
else if(a<=100,a<200)
{
cout<<" "<<endl;
cout<<"    做50张卷子!"<<endl;
cout<<"     游戏结束！"<<endl;
cout<<" "<<endl;
cout<<"*******************";
}
else if(a<=200,a<280)
{
cout<<" "<<endl;
cout<<"    做10张卷子!"<<endl;
cout<<"     游戏结束！"<<endl;
cout<<" "<<endl;
cout<<"*******************";

}
else if(a<=280,a<299)
{
cout<<" "<<endl;
cout<<"      买乐高!"<<endl;
cout<<"     游戏结束！"<<endl;
cout<<" "<<endl;
cout<<"*******************";
}
else if(a==300,a<301)
{
cout<<" "<<endl;
cout<<"      买iPad!"<<endl;
cout<<"     游戏结束！"<<endl;
cout<<" "<<endl;
cout<<"*******************";
}
else if(a==301,a<1000000000000000)
{
cout<<" "<<endl;
cout<<"       错误！"<<endl;
cout<<"*******************";

 
 
   
}
    return 2;
    }
以上为源代码，希望能帮助到广大家长，嘻嘻

类似于“if(a<=0,a<50)”这种错误，如果编译器不报警告，你应该把编译器卸载掉；如果编译器报了但你不在意，你应该把自己卸载掉。
另外代码不排版，……

还有，“else if(a==301,a<1000000000000000)”，如果你的 int a 最大有效值达不到1000000000000000，那它是恒成立的