I need help figuring out what's wrong with the following code:

My output should be this :

9999991123332545854565

19999977555531536019996

3091133555689134

#include

using namespace std;

string add(string small, string big) {

string result = "";

int carry = 0;

if(small.length()>big.length()){

swap(small,big);

}

for (int i=0; i < big.length(); i++){

small = '0'+ small;

}

for (int i=big.length()-1; i>=0 ; i-- ){

int value =

big [i] - '0' + small [i] - '0' + carry;

if (value < 10){

result = (char) (value + '0') + result;

}

else {

result = (char)(value % 10) + result;

carry = 1;

}

if (carry == 1)

result = "1" + result;

}

return result;

}

int main() {

cout << add("2345566777844567", "9999988777765768009998") << endl;

cout << add("9999988777765768009998", "9999988777765768009998") << endl;

cout << add("2345566777844567", "745566777844567") << endl;

cout << "End of Program." << endl;

return 0;

}