本地通过但测评机RE

本地编译通过了但是使用洛谷的C++11过不了，求大神帮忙

#include<bits/stdc++.h>
#include<sstream>
using namespace std;
int calc(int a,int b,char method);
char show(char x);
int main(){
    int i;
    cin>>i;
    char flag;
    vector<string> results;
    string rr="";
    for(int j=0;j<i;j++){
        char str[500]={0};
        fflush(stdin);
        gets(str);
        if(str[0]=='a'||str[0]=='b'||str[0]=='c'){
            flag=str[0]; 
            istringstream ss(str);
            vector<string> words;
            string word;
            while(ss >> word) {
                words.push_back(word);
            }           
            int a=stoi(words[1]);
            int b=stoi(words[2]);
            int r=calc(a,b,flag);
            //cout<<a<<show(flag)<<b<<"="<<r;

            string temp;
            temp+=to_string(a); 
            temp+=show(flag);
            temp+=to_string(b); 
            temp+="=";
            temp+=to_string(r); 
            int length=temp.length();
            rr+=temp;
            rr+='\n';
            rr+=to_string(length);
            rr+='\n';
            continue;
        }else{
            istringstream ss(str);
            vector<string> words;
            string word;
            while(ss >> word) {
                words.push_back(word);
            }
            int a=stoi(words[0]);
            int b=stoi(words[1]);
            int r=calc(a,b,flag);
            //cout<<a<<show(flag)<<b<<"="<<r;
            string temp;
            temp+=to_string(a); 
            temp+=show(flag);
            temp+=to_string(b); 
            temp+="=";
            temp+=to_string(r); 
            int length=temp.length();
            rr+=temp;
            rr+='\n';
            rr+=to_string(length);
            rr+='\n';
            continue;       
        }
    }
    cout<<rr;
    return 0;
}

int calc(int a,int b,char method){
    if(method=='a'){
        return a+b;
    } 
    if(method=='b'){
        return a-b;
    }
    if(method=='c'){
        return a*b;
    }
}
char show(char x){
    if(x=='a'){
        return '+';
    }
    if(x=='b'){
        return '-';
    }
    if(x=='c'){
        return '*';
    }
}