WA on http://www.spoj.com/problems/CHI_BINARY/

[angrypig298]

#include<iostream>
#include<string>

using namespace std;

string sodu;
int gr(string, string);
string cong(string, string);
string tru(string, string);
string nhan(string, string);
string chia(string, string);

int main()
{
	string soTest;
	string a, b;
	int op;
	cin>>soTest;
	while(soTest[0]=='0' && soTest.length() > 1) soTest.erase(soTest.begin(), soTest.begin()+1);
	while(soTest != "0"){
		soTest = tru(soTest, "1");
		cin>>op>>a>>b;
		while(a[0]=='0' && a.length() > 1) a.erase(a.begin(), a.begin()+1);
		while(b[0]=='0' && b.length() > 1) b.erase(b.begin(), b.begin()+1);
		if(op == 0) cout<<gr(a, b)<<endl;
		else if(op == 1) cout<<cong(a, b)<<endl;
		else if(op == 10) cout<<tru(a, b)<<endl;
		else if(op == 11) cout<<nhan(a, b)<<endl;
		else if(op == 100) cout<<chia(a, b)<<" "<<sodu<<endl;
	}
	return 0;
}

int gr(string a, string b)
{
	long la = a.length();
	long lb = b.length();
	if(la > lb) return 1;
	else if(la < lb) return 0;
	else{
		for(long i=0; i<la; i++){
			if(a[i] > b[i]) return 1;
			else if(a[i] < b[i]) return 0;
		}
		return 0;
	}
}

char exor(char a, char b)
{
	if(a != b) return '1';
	else return '0';
}

string cong(string a, string b)
{
	char out = '0', t;
	long la = a.length();
	long lb = b.length();
	string c = "";
	while(la > 0 && lb > 0){
		la--;
		lb--;
		t = exor(a[la], b[lb]);
		c = exor(t, out) + c;
		if((a[la]==b[lb] && a[la]=='1') || (t==out && out=='1')) out = '1';
		else out = '0';
	}
	while(la > 0){
		la--;
		c = exor(a[la], out) + c;
		if(a[la]==out && out=='1') out = '1';
		else out = '0';
	}
	while(lb > 0){
		lb--;
		c = exor(b[lb], out) + c;
		if(b[lb]==out && out=='1') out = '1';
		else out = '0';
	}
	if(out == '1') c = '1' + c;
	return c;
}

string tru(string a, string b)
{
	char out = '0', t;
	long la = a.length();
	long lb = b.length();
	string c = "";
	while(la > 0 && lb > 0){
		la--;
		lb--;
		t = exor(a[la], b[lb]);
		c = exor(t, out) + c;
		if((a[la]=='0' && b[lb]=='1') || (t=='0' && out=='1')) out = '1';
		else out = '0';
	}
	while(la > 0){
		la--;
		c = exor(a[la], out) + c;
		if(a[la]=='0' && out=='1') out = '1';
		else out = '0';
	}
	while(lb > 0){
		lb--;
		c = exor(exor('0', b[lb]), out) + c;
		if(b[lb]=='1' || (b[lb]=='0' && out=='1')) out = '1';
		else out = '0';
	}
	while(c[0]=='0' && c.length() > 1) c.erase(c.begin(), c.begin()+1);
	return c;
}

string nhan(string a, string b)
{
	long la = a.length();
	long lb = b.length();
	string d = a;
	string c = "0";
	while(lb>0){
		lb--;
		if(b[lb]=='1') c = cong(c, d);
		d += '0';
	}
	return c;
}

string chia(string a, string b)
{
	if(b == "0"){
		sodu = "0";
		return "0";
	}
	else if(!gr(a, b) && a!=b){
		sodu = a;
		return "0";
	}
	else if(a==b){
		sodu = "0";
		return "1";
	}
	else{
		long la = a.length();
		long lb = b.length();
		string c = "";
		sodu = "";
		for(long i = 0; i < lb; i++) sodu += a[i];
		long tro = lb-1;
		if(!gr(sodu, b) && sodu != b) sodu += a[++tro];
		while(tro < la-1){
			tro++;
			if(gr(sodu, b) || sodu == b){
				c += '1';
				string t = tru(sodu, b);
				if(t != "0") sodu = t + a[tro];
				else sodu = a[tro];
			}
			else{
				c += '0';
				sodu += a[tro];
			}
		}
		if(gr(sodu, b) || sodu == b){
			c += '1';
			sodu = tru(sodu, b);
		}
		else c += '0';
		return c;
	}
}

I am a newbie.
I can’t find anything wrong. Please help me! Thank you!