UVa 713 Adding Reversed Numbers Solution

#include<iostream>
#include<string>
#include<cstring>
#include<sstream>
#include<cctype>
#include<string.h>
#include<algorithm>
#include<cmath>
#include<stack>
#include<fstream>
#include<cstdlib>
#include<iomanip>
#include<vector>
#include<map>
#include<set>
using namespace std;


string rev(string a){
                    int i,j;
                    string b="";
                    for(i=0,j=a.length()-1;i<a.length();i++,j--)
                            b+=a[j];
                    return b;
                    }
string add(string a, string b){//not for regular addition
                                int i,j,x,y,sum,s,temp=0,p,f=0;
                                string c="";
                                string t="";
                                string e,r;
                                if(a.length()<b.length()){
                                                         e=a;
                                                         a=b;
                                                         b=e;
                                                         }
                                for(i=0;i<a.length();i++)
                                    {
                                    if(i<b.length())
                                            {
                                            x=a[i]-'0';
                                            y=b[i]-'0';
                                            sum=x+y+temp;
                                            s=sum%10;
                                            c+=s+'0';
                                            temp=0;
                                            if(sum>9) temp=1;
                                            if(i==a.length()-1 && temp==1)
                                                c+='1';
                                            }
                                    else {
                                         x=a[i]-'0';
                                         sum=temp+x;
                                         s=sum%10;
                                         c+=s+'0';
                                         temp=0;
                                         if(sum>9) temp=1;
                                            if(i==a.length()-1 && temp==1)
                                                c+='1';
                                         }
                                    }
                                for(i=0;i<c.length();i++)
                                    {
                                    if(f==0){
                                            if(c[i]!='0'){
                                                         f++;
                                                         t+=c[i];
                                                         }
                                            else if(i==c.length()-1) t+=c[i];
                                            }
                                    else {
                                         t+=c[i];

                                         }
                                    }
                                return t;
                                }
int main()
{
string a,b;
int x,i;
while(cin>>x)
    {
    for(i=0;i<x;i++)
        {
        cin>>a>>b;
        cout<<add(a,b)<<endl;
        }
    }
return 0;
}