Question

Why does the following code print out "0 0 0 0 0 0 0 "? I was expecting "1 3 6 10 15 21 28 ".

#include <iostream>

using namespace std;

void PrefixSum(float * input, float * output, int n){
    float sum = 0;
    for (int i=0;i<n;i++){
        float value = input[i];
        sum += value;
        output[n] = sum;
    }    
}


int main(int argc, const char * argv[])
{
    float input[] = {1,2,3,4,5,6,7};
    float output[] = {0,0,0,0,0,0,0};
    PrefixSum(input, output, 7);
    for (int i=0;i<7;i++){
        cout << output[i] << " ";
    }
    return 0;
}

Answer 1

Change output[n] to output[i] instead, you’re not writing to any index in the array since output[7] is out of bounds. i is your loop counter not n