Executing print in standard output causing random assigning of value in array

Question

I'm sorry if this is a silly question. I have written the following piece of code for coin change problem.

#include <iostream>
using namespace std;

int coinChange(int coins[], int n, int amount)
{
int combinations[amount + 1];
combinations[0] = 1;

int start;
for(int i = 0; i < n; i++)
{
    start = coins[i];
    int coin = coins[i];
    for(int j = start; j < amount + 1; j++)
    {
        if(j >= coin)
        {
            combinations[j] += combinations[j - coin];
        }
    }
    for(int j = 0; j < amount + 1; j++)
        cout << combinations[j] << " ";
    cout << endl;
}

return combinations[amount];
}

int main(int argc, char const *argv[])
{
int coins[] = {1, 2, 5};
int n = sizeof(coins)/sizeof(coins[0]);

int amount = 12;

// cout << "Total combinations: ";
cout << coinChange(coins, n, amount) << endl;

return 0;
}

The code works fine and provides me the correct output as shown below.

1 1 1 1 1 1 1 1 1 1 1 1 1 
1 1 2 2 3 3 4 4 5 5 6 6 7 
1 1 2 2 3 4 5 6 7 8 10 11 13 
13

However, If I uncomment the line cout << "Total combinations: "; just above the function calling in the main function, the program gives me bizzare outputs.

Total combinations: 1 32768 32768 32768 44137 44137 44137 44137 196418491 196418492 -790461916 -790429149 619621115 
1 32768 32769 65536 76906 109673 121043 153810 196539534 196572302 -593922382 -593856847 25698733 
1 32768 32769 65536 76906 109674 153811 186579 196605070 196649208 -593812708 -593703036 25885312 
25885312

Is executing cout before function calling causing this random outputs? Or is this a problem for my version of compiler?

Answer 1

What about initialize (to zero?) combinations ?

Something like

int combinations[amount + 1] {};

Otherwise the initial values of combinations[i] are undefined indeterminate, so are is undefined the final values behavior of the program (correction from Shafik Yaghmour; thanks!)

Answer 2

Do this in your coinChange function.

int combinations[amount + 1]{};
combinations[0] = 1;

int start;
for(int i = 0; i < n; i++)
{
    start = coins[i];
    int coin = coins[i];
    for(int j = start; j < amount + 1; j++)
    {
        if(j >= coin)
        {
            combinations[j] += combinations[j - coin];
        }
    }
    for(int j = 0; j < amount + 1; j++)
        cout << combinations[j] << " ";
    cout << endl;
}

Now uncomment the line and run. The basic problem is when you create the combinations array, you have to initialize the elements to 0 . If you don't, they may be all 0 by a lucky coincidence, but you can't guarantee that.

EDIT : Using empty initializer list to initilize array with zeros as max66 suggested.