The question is about printing digits of two digit number n, I'm encountering a runtime error

Question

Given a two-digit number n, print both the digits of the number.

Input Format: The first line indicating the number of test cases T.

Next T lines will each contain a single number ni.

Output Format: T lines each containing two digits of the number ni separated by space.

Constraints

1 <= T <= 100000 10 <= ni <= 99

Error: Runtime Error (SIGSEGV)

I'm not able to pinpoint, where the problem is in the code as it is working fine for a two numbers while it gives the runtime error for 4 or more numbers. Is there another way of doing this problem other than using for loop twice?

#include <bits/stdc++.h>
using namespace std;

int main()
{
    int t;
    int arr[t];
    cin>>t;
    for(int i=0;i<t;i++)
    {
        cin>>arr[i];
    }
    int c;
    int b;
    for(int i=0;i<t;i++)
    {
        c=(arr[i]/10);
        if(c!=0)
        {
            b=arr[i]%(c*10);
        }
        else 
        {
            b=arr[i];
        }
        cout<<c<<" "<<b<<endl;
    }
    
    
    return 0;
}

What do you think that lines like `1 <= t<= 100000;` or `10 <= arr[i]<=99;` accomplish? — molbdnilo, Nov 29 '21 at 08:55
@molbdnilo there was a limit in the question, to be precise a contraint, idk if i used it correctly. — Manya Garg, Nov 29 '21 at 08:57
Yes, but what do you think those expressions do on their own? You have never seen examples of C++ that do anything like that, and they don't even mean the comparisons you believe that they mean. (Definitions of input limits usually mean that you are guaranteed that those hold, not that you need to check.) — molbdnilo, Nov 29 '21 at 08:58
@justANewbie ok, i'll look into how to limit it correctly, is it the reson why i'm encountering the runtime error? — Manya Garg, Nov 29 '21 at 08:59
Think about what the value of `t` is at the point where you declare `int arr[t];` — molbdnilo, Nov 29 '21 at 09:00
Read the number(s) as `std::string` process as strings; nothing in the question tells you to use integers. — Richard Critten, Nov 29 '21 at 09:02
In future, whenever you get a crash and you're not sure why, use a debugger - it will tell you where the problem is (usually). — cmannett85, Nov 29 '21 at 09:05
Shorter version: `while (t--) { int x; cin >> x; cout << x / 10 << ' ' << x % 10 << endl; }` — molbdnilo, Nov 29 '21 at 09:10

score 0 · Accepted Answer · answered Nov 29 '21 at 09:16

Fist, you declare t, but do not initialize it, so it is uninitialized. Trying to use the value leads to undefined behavior.

Second, VLA is not valid C++, see here. You have to use std::vector instead.

Third, you don't need to use an int.

So, you should do:

#include <iostream>
#include <vector>
#include <string>
int main()
{
    int t{};
    std::cin >> t;
    std::vector<std::string> arr(t);
    for(int i = 0; i < t; i++)
    {
        std::cin >> arr[i];
    }
    for(const auto &i : arr)
    {
        std::cout << i[0] << ' ' << i[1] << '\n';
    }

}

The question is about printing digits of two digit number n, I'm encountering a runtime error

1 Answers1