Find sum of elements in the array

Question

I have this program which worked find in my college lab, but when I run it at my home it gives different result

#include <stdio.h>
int main(int argc, char* argv[]) {
        const int size=100;
        int n, sum=0;
        int* A = (int*)malloc( sizeof(int)*size );
        for (n=size-1; n>0; n--)
                A[n] = n;

        for (n=0;n<size; n++)
                sum += A[n];

        printf ("sum=%d\n", sum);
        return 0;

}

I'm expecting 4950 as result but I keep getting different result like 112133223 . Why is this happening ?

Answer 1

You are not assigning value to A[0] . As a result of this A[0] will have garbage value which is getting added to sum .

Change

for (n=size-1; n>0; n--)
               ^^^

to

for (n=size-1; n>=0; n--)
               ^^^^

Also you need to free the dynamically allocated memory by doing:

free(A);

before you return.

Answer 2

You never assign a value to A[0] - the first loop ends to quickly. However you do include this unassigned value in the summation.

Answer 3

A[0] is undefined:

for (n=size-1; n>0; n--)

should be

for (n=size-1; n>=0; n--)

Answer 4

Just because you didn't put any value in first element, you had garbage there. thus, some random number in sum.

#include <stdio.h>
#include<stdlib.h> //for malloc
int main(int argc, char* argv[]) {
        const int size=100;
        int n, sum=0;
        int* A = (int*)malloc( sizeof(int)*size );
        for (n=size-1; n>=0; n--) //you forgot '='
                A[n] = n;

        for (n=0;n<size; n++)
                sum += A[n];

        printf ("sum=%d\n", sum);
        return 0;

}

Answer 5

it worked fine for me. I executed it using GCC. this is the program i ran:

#include <stdio.h>
#include <malloc.h>
int main(int argc, char* argv[]) {
    const int size=100;
    int n, sum=0;
    int* A = (int*)malloc( sizeof(int)*size );
    for (n=size-1; n>0; n--)
            A[n] = n;

    for (n=0;n<size; n++)
            sum += A[n];

    printf ("sum=%d\n", sum);
    return 0;
}