CODEWITHSUNDEEP
c++arrays
Richard Wei
Richard Wei

Reputation: 97

Why are random values generated for some elements in a two-dimensional int array?

I've been reading up on some Dynamic Programming. It works (at least from my understanding) by generating a two-dimensional integer array to store solutions to subproblems.

In C++, you can declare a two-dimensional, 10x10 array like this: int d[10][10];.

Now I thought by declaring the array without assigning any values, all the values in the array should be 0, however, the values in the array are a weird combination of large positive or negative numbers and zeros.

I have tried this piece of code here to test outcomes on different compilers:

#include<iostream>
using namespace std;
int main()
{    
    int d[10][10];
    for (int i =0; i < 10; i++){
        for (int j = 0; j < 10; j++){
            cout << d[i][j] << " ";
        }
        cout << endl;
    }
    return 0;
}

Results:

cpp.sh

Test 1:

First CPP.SH test

Test 2:

Second CPP.SH test

OnlineGDB

Test 1:

First OnlineGDB test

Test 2:

Second OnlineGDB test

Visual Studio

Test 1:

First Visual Studio test

Test 2:

Second Visual Studio test

As you can see, CPP.SH and OnlineGDB both generate seemingly arbitrary numbers in the place of some values while others are 0. The only exception being Visual Studio. Is there an explanation for where these seemingly arbitrary numbers come from? Why is Visual Studio the only compiler that doesn't have this kind of behavior? Thanks.

Upvotes: 0

Views: 946

Answers (2)

Silverfang
Silverfang

Reputation: 359

There is no default value for int when declared as non static variable in most cases. That is why it is giving such random values. just use this int array[ROW][COLUMN]={0}; It will give the output that you are looking for.

Upvotes: 0

robthebloke
robthebloke

Reputation: 9678

Because the memory has not yet been initialised, so you are seeing whatever values happen to be left in that memory. If you want to initialise to zero, you can do:

    int d[10][10] {};

Upvotes: 1

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