CODEWITHSUNDEEP
c++
Aradhya
Aradhya

Reputation: 53

Why is my c++ program crashing?

#include <iostream>
#include <vector>
using namespace std;
int m,n;
vector<vector<int> > name(m,vector<int>(n));
int main()
{
    cin>>m>>n;
    for ( int i=0;i<m;i++)
    {
        for( int j=0;j<n;j++)
            cin>>name[i][j];
    }
}

Every time I give the input m and n, it crashes! What I am trying to do is to give the input to a 2 dimensional array of m rows and n columns.

Upvotes: 0

Views: 106

Answers (3)

Arun Sharma
Arun Sharma

Reputation: 517

Error is you are trying to access the index out of bound

Because your name is not a 2D vector.

use this code instead to make name a 2D vector.

vector < vector <int> > name;
vector<int > col;
int r, c;
void main()
{

    cin >> r;
    cin >> c;
    for (int i = 0; i < c; i++)
    {
        col.push_back(i);//push i to col just to make it size of columns needed
    }

    for (int i = 0; i < r; i++)
    {
        name.push_back(col);//pushing vector col of size c into name to 
        //make it a 2D vecotr
    }
    //now name is a 2D vector with r rows of each c column
    cout << "\nNow Enter values";
    for (int i = 0; i < r; i++)
    {
        for (int j = 0; j < c; j++)
        {
            cin >> name[i][j];//input values
        }
    }

    getch();


}

Upvotes: 1

fasked
fasked

Reputation: 3645

Because of you have run out of bounds.

The name vector is global variable, so it is initialised at the moment of program starting, even before main function. Also integer global variables are initialised with 0 in C++. So the name vector has zero size.

After reading n and m values you need to resize the vector.

Upvotes: 5

Benjamin Lindley
Benjamin Lindley

Reputation: 103693

You need to initialize your vector (or resize it) after you read the values for m and n. As you have it, m and n are 0* when the vector is initialized, so the size of the vector is 0.

*this is only the case because you placed them at global scope. if placed in a function, they would be uninitialized, and it would be undefined behavior to use their values

Upvotes: 5

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