Probleem with substr in c++ - c++

Question

I made binary calculator. It works, but only when numbers doesnt start with 0. if yes, it shows this:
How I should repair the program, please? (vysledek means result)
Part of code with substr:
while(vysledek[0] == '0')
{
vysledek = vysledek.substr(1, vysledek.length());
w++;
}
int aa;
aa = p-w;
for(o; o < aa; o++)
{
cout << vysledek[o];
}
Whole program:`
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
using namespace std;
int main()
{
cout << "Zadejte dve binarni cisla:" << endl;
string cislo1, cislo2;
cin >> cislo1 >> cislo2;
int c = 0;
for (c; c < cislo1.length(); c++)
{
if ((cislo1[c] == '0') || (cislo1[c] == '1'))
{
continue;
}
else
{
cout << "Nespravny vstup.";
return 0;
}
}
int d = 0;
for (d; d < cislo2.length(); d++)
{
if ((cislo2[d] == '0') || (cislo2[d] == '1'))
{
continue;
}
else
{
cout << "Nespravny vstup.";
return 0;
}
}
string stringS2 = "";
for(unsigned i = 0; i < cislo1.length(); i++)
{
stringS2 += cislo1[cislo1.length()-1-i];
}
cislo1 = stringS2;
string stringS3 = "";
for(unsigned i = 0; i < cislo2.length(); i++)
{
stringS3 += cislo2[cislo2.length()-1-i];
}
cislo2 = stringS3;
/*
cout << cislo1 << endl;
cout << cislo2 << endl;
cout << cislo1.length() << endl;
cout << cislo2.length() << endl;
*/
int p;
if (cislo1.length() > cislo2.length())
{
p = cislo1.length();
int f = cislo2.length();
for(f; f < cislo1.length(); f++)
{
cislo2[f] = '0';
}
}
else
{
p = cislo2.length();
int f = cislo1.length();
for(f; f < cislo2.length(); f++)
{
cislo1[f] = '0';
}
}
int e = 0;
//cout << p << endl;
string vysledek;
int t;
t = (p - 1);
cislo1[p];
cislo2[p];
for(e; e < p; e++)
{
/*nasledujici podminky jsou pro pripad, kdy cisla maji odlisny pocet znaku
if(cislo1[e] == NULL)
{
cislo1[e] == '0';
}
if(cislo2[e] == NULL)
{
cislo2[e] == '0';
}*/
if (cislo1[e] == '0' && cislo2[e] == '0')
{
if ((cislo1[e-1] == '1' && cislo2[e-1] == '1')|| ((cislo1[e-1] == '0' && cislo2[e-1] == '1')&& vysledek[t+1] == '0') || ((cislo1[e-1] == '1' && cislo2[e-1] == '0')&& vysledek[t+1] == '0') || ((cislo1[e-1] == '1' && cislo2[e-1] == '1')&& vysledek[t+1] == '1') )
{
vysledek[t] = '1';
}
else
{
vysledek[t] = '0';
}
//cout << vysledek[t] << endl;
t--;
}
else if ((cislo1[e] == '1' && cislo2[e] == '0') || (cislo1[e] == '0' && cislo2[e] == '1') )
{
if ((cislo1[e-1] == '1' && cislo2[e-1] == '1') || ((cislo1[e-1] == '0' && cislo2[e-1] == '1')&& vysledek[t+1] == '0') || ((cislo1[e-1] == '1' && cislo2[e-1] == '0')&& vysledek[t+1] == '0') || ((cislo1[e-1] == '1' && cislo2[e-1] == '1')&& vysledek[t+1] == '1'))
{
vysledek[t] = '0';
}
else
{
vysledek[t] = '1';
}
// cout << vysledek[t] << endl;
t--;
}
else if (cislo1[e] == '1' && cislo2[e] == '1')
{
if ((cislo1[e-1] == '1' && cislo2[e-1] == '1') || ((cislo1[e-1] == '0' && cislo2[e-1] == '1')&& vysledek[t+1] == '0') || ((cislo1[e-1] == '1' && cislo2[e-1] == '0')&& vysledek[t+1] == '0') || ((cislo1[e-1] == '1' && cislo2[e-1] == '1')&& vysledek[t+1] == '1'))
{
vysledek[t] = '1';
}
else
{
vysledek[t] = '0';
}
//cout << vysledek[t] << endl;
t--;
}
}
cout << "Soucet: ";
int u;
u = (p - 1);
if(((cislo1[u] == '0' && cislo2[u] == '1')&& vysledek[0] == '0') || ((cislo1[u] == '1' && cislo2[u] == '0')&& vysledek[0] == '0') || (cislo1[u] == '1' && cislo2[u] == '1') )
cout << '1';
int o = 0;
int z;
int w = 0;
while(vysledek[0] == '0')
{
vysledek = vysledek.substr(1, vysledek.length());
w++;
}
int aa;
aa = p-w;
for(o; o < aa; o++)
{
cout << vysledek[o];
}
return 0;
}
`

Answer 1

string vysledek; creates an empty string. It is never given any other size.
All following uses of vysledek[t] and vysledek.substr are all out of range.