问题标题: 酷町堂：哪错了？？？？？

#include<bits/stdc++.h>   
using namespace std;     
int main(){             
    system("color F5");
    cout<<"小小计算器\n";
    cout<<"版本2.11，作者:徐烨奎\n"; 
    cout<<"数不能超过7位数!\n";   
    char c; 
    long double a,b;
    cout<<"请输入一个符号(+加号,-减号,*乘号,/除号)\n";
    cin>>c;
    cout<<"请输入两个数\n"; 
    cin>>a>>b;
    if(a>=1000000||b>=1000000){
        system("cls");
        cout<<"数字超标";
        return 0;
    }
     system("cls");
    if(c=='+'||c=='-'||c=='*'||c=='/'){  
    cout<<"计算结束\n";   

    if(c=='+'){
    cout<<a<<"+"<<b<<"="<<a+b;
    }
    if(c=='-'){
    cout<<a<<"-"<<b<<"="<<a-b;
    }
    if(c=='*'){
    cout<<a<<"*"<<b<<"="<<a*b;
    }
    if(c=='/'){
    cout<<a<<"/"<<b<<"="<<a/b;
    }
}
    else if(c!='+'&&c!='-'&&c!='*'&&c!='/'){
    system("cls");  
    cout<<"输入错误\n请重新输入\n";    
    char c; 
    double a,b;
    cout<<"请输入一个符号(+加号,-减号,*乘号,/除号)\n";
    cin>>c;
    cout<<"请输入两个数\n";  
    cin>>a>>b;
   if(c=='+'||c=='-'||c=='*'||c=='/'){
        cout<<"计算结束\n";       
    if(c=='+'){
    cout<<a<<"+"<<b<<"="<<a+b;
    }
    if(c=='-'){
    cout<<a<<"-"<<b<<"="<<a-b;
    }
    if(c=='*'){
    cout<<a<<"*"<<b<<"="<<a*b;
    }
    if(c=='/'){
    cout<<a<<"/"<<b<<"="<<a/b;
    } 
}
}
    system("cls");
    if(c!='+'&&c!='-'&&c!='*'&&c!='/'){
    system("cls");  
    cout<<"输入错误\n请重新输入\n";    
    char c; 
    double a,b;
    cout<<"请输入一个符号(+加号,-减号,*乘号,/除号)\n";
    cin>>c;
    cout<<"请输入两个数\n";  
    cin>>a>>b;
    system("cls");
    if(c=='+'||c=='-'||c=='*'||c=='/'){
        cout<<"计算结束\n"; 
        }   
    if(c=='+'){
    cout<<a<<"+"<<b<<"="<<a+b;
    }
    if(c=='-'){
    cout<<a<<"-"<<b<<"="<<a-b;
    }
    if(c=='*'){
    cout<<a<<"*"<<b<<"="<<a*b;
    }
    if(c=='/'){
    cout<<a<<"/"<<b<<"="<<a/b;
    }
    else if(c!='+'&&c!='-'&&c!='*'&&c!='/'){
        cout<<"输入错误";
        return 0; 
    } 
    } 
    system("color 5F");
    return 0;            
}