terminate called after throwing an instance of 'std::out_of_range' c++

Question

my assignment is to do the following:

1. Generate some rows of numeric digits. Use the random number generator.

2. Ask the user for the number of rows and columns of digits. 2x4 would look like this...

   0655

   6476

3. Treat each row of digits as a single number. Show the sum using addition. Example:

   0655

   6476

   7131 < sum of 0655 and 6476

Now I've gotten it to mostly work with the code below.

#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;

int main(int argc, char *argv[])
{
    int x;
    int y;
    int total = 0;
    int sum[100];
    int num;
    string val= "";
    srand((unsigned)time(NULL));
    cout << "\nHow many rows?\n" << endl;
    cin >> x;
    cout << "\nHow many columns?\n" << endl;
    cin >> y;
    int rows = x;
    int columns = y;
    for (int i=0; i<rows; i++) {
        cout << "    ";
        for (int j = 0; j < columns; j++) {
            int r = rand() % 10;
            sum[j]= r;
            if (j == columns - 1){
                for (int k = 0; k <= j; k++ ) {
                    val = val + to_string(sum[k]);
                }
                num = stoi(val);
                total += num;
                val = "";
            }
            cout << r;
        }
        cout << endl;
    }
    cout << "    "<< total << endl;
    cout << endl;
    cout << "program complete.\n" << endl;
    return 0;
}

However, whenever the y value from user input is 10 or higher I get the error:

terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

No errors from any x value from user input as far as I can tell.

Is this just a bad way of doing this? Should I scrap the code and try a different method?

Answer 1

The range of 32bit integer is 2e9+. Use 'long long' instead of int.
But wait, 'stoi()' will not work then.
You do not need to use string as well as stoi() function. I have changed the data type to long long. Have a look at this:

#include <iostream>
#include <cstdlib>
#include <string>
#include <time.h>
typedef long long ll;
using namespace std;

int main(int argc, char *argv[])
{
    ll x;
    ll y;
    ll total = 0;
    ll sum[100];
    ll num;
    srand((unsigned)time(NULL));
    cout << "\nHow many rows?\n" << endl;
    cin >> x;
    cout << "\nHow many columns?\n" << endl;
    cin >> y;
    ll rows = x;
    ll columns = y;
    for (int i=0; i<rows; i++) {
        cout << "    ";
        for (int j = 0; j < columns; j++) {
            ll r = rand() % 10;
            sum[j]= r;
            if (j == columns - 1){
                ll val= 0;
                for (int k = 0; k <= j; k++ ) {
                    val = val*10 + sum[k];
                }
                num = val;
                total += num;
            }
            cout << r;
        }
        cout << endl;
    }
    cout << "    "<< total << endl;
    cout << endl;
    cout << "program complete.\n" << endl;
    return 0;
}