C++ convert string to int if numeric, else return 0

Question

My code asks user to enter coordinates and if the input is q, the program stops and otherwise, it checks if the input is numeric.

If x and y are both numeric, stoi_with_check converts them from string to int. This is because later I need to use coordinates as int when making a matrix.

If x or y is not numeric, stoi_with_check returns 0.

On lines 44 and 45, I'm not sure how this stoi_with_check function should be used, if I want to check both strings, x and y.

Thanks for your help.

#include <iostream>
#include <string.h>

using namespace std;

unsigned int stoi_with_check(const string& str) // if numeric -> convert string to int, if not numeric -> return 0
{
    bool is_numeric = true;
    for(unsigned int i = 0; i < str.length(); ++i)
    {
        if(not isdigit(str.at(i)))
        {
            is_numeric = false;
            break;
        }
    }
    if(is_numeric)
    {
        return stoi(str);
    }
    else
    {
        return 0;
    }
}

int main()

{
    string x, y;

        while (true) {
            cout << "Enter coordinates (x, y): ";
            cin >> x;
            if (x == "q" or x == "Q") {
                cout << "Quitting" << endl;
                exit(0);
            }

            cin >> y;
            // x and y are now strings
            // Next convert them to ints if they are numeric
            // If they are not numeric, return value 0
            stoi_with_check(x);
            stoi_with_check(y);

            // next print board by using int x and int y
        }
    }

You never store the result of these function calls? Just use another set of variables int ix, iy; to do that. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Aug 17, 2022 at 10:25
Use the fact that std::stoi's can throw exceptions : en.cppreference.com/w/cpp/string/basic_string/stol. Thus : try { return std::stoi(str); } catch( const std::exception&) { return 0; } . — Pepijn Kramer
– Pepijn Kramer, Commented Aug 17, 2022 at 10:32
A tip on style: for (unsigned i = 0; ii < str.length(); ++i) if (!isdigit(str[i])) return 0; is much clearer. For several reasons. — Pete Becker
– Pete Becker, Commented Aug 17, 2022 at 12:39

Lajos Arpad · Accepted Answer · 2022-08-17 10:33:15Z

1

This is how you could do it:

int X = stoi_with_check(x);
int Y = stoi_with_check(y);

if (X && Y) { //None of them is 0
    //Do your stuff
}

Basically you store your would-be-coordinates and if they are valid, process them.

answered Aug 17, 2022 at 10:33

Lajos Arpad

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