Question

It might sound stupid, but I was just wondering how can I parse a string to an integer in C++?

This is for a school project, and the explanation sheet says :
“Only the use of iostream and string classes and system() function is permitted; The use of any other class or function is prohibited.”

I have searched around a bit, but the only suggestions I found are using classes like atoi or atof.

The input string is already checked for error before the parsing, so it will always only contain an integer.

I wouldn’t mind doing the parsing manually with conditionals, but I don’t think it would be my teacher’s (or anyone’s) preferred way.

Thanks a bunch if you can help.

Answer 1

#include <iostream>
#include <string>

int stringToInt(const std::string &text)
{
    int number = 0;

    int powerIndex = 1;

    for (int i = text.length() - 1; i >= 0; i--)
    {
        number += powerIndex * (text.at(i) - '0');

        powerIndex *= 10;
    }

    return number;
}

std::string intToString (int number)
{
    std::string text = "";

    int numberHolder = number;

    while (numberHolder)
    {
        char digit = (numberHolder % 10) + '0';

        text = digit + text;

        numberHolder /= 10;
    }

    return text;

}
int main ()
{
    //Testing...

    int number = stringToInt("123");

    std::string text = intToString(456);

    std::cout << number << "\n" << text << "\n";

    return 0;
}