问题标题: 这个计算器有缺点吗

#include<bits/stdc++.h>     
using namespace std;     
int main()              
{
     system("color F5");
     cout<<"小小计算器\n";
     cout<<"温馨提示:如果三次输入错误，则计算结束\n" ;     
     char c; 
     double a,b;
     cout<<"请输入一个符号\n";
     cin>>c;
     cout<<"请输入两个数\n"; 
     cin>>a>>b;
     system("cls");
     if(c!='+'&&c!='-'&&c!='*'&&c!='/'){
     cout<<"输入错误\n请从新输入\n";   
     char c; 
     double a,b;
     cin>>c; 
     cin>>a>>b;
     system("cls");
     if(c!='+'&&c!='-'&&c!='*'&&c!='/'){
     cout<<"输入错误\n请从新输入\n";
     char c; 
     double a,b;
     cin>>c; 
     cin>>a>>b;
     system("cls");
     if(c=='+'){
     cout<<a+b;
}
else if(c=='-'){
    cout<<a-b;
}
else if(c=='*'){
    cout<<a*b;
}
else if(c=='/'){
    cout<<a/b;
}
}
else if(c!='+'&&c!='-'&&c!='*'&&c!='/'){
    return 0;
}
else if(c=='+'){
    cout<<a+b;
}
else if(c=='-'){
    cout<<a-b;
}
else if(c=='*'){
    cout<<a*b;
}
else if(c=='/'){
    cout<<a/b;
}
system("color 5F");
     if(c=='+'){
    cout<<a+b;
}
else if(c=='-'){
    cout<<a-b;
}
else if(c=='*'){
    cout<<a*b;
}
else if(c=='/'){
    cout<<a/b;
}
}
else if(c=='+'){
    cout<<a+b;
}
else if(c=='-'){
    cout<<a-b;
}
else if(c=='*'){
    cout<<a*b;
}
else if(c=='/'){
    cout<<a/b;
}
system("color 5F");
    return 0;            
}