Why array values are different from assigned values C program

Question

I wrote a small code to that takes an array of 10 values, passes the array to a function which doubles each value. The array prints expected values (double) within the function. Back in the main function, the output printed has garbage values for index 1, 2 and 3 in the for loop meant to print all values. Why are these values altered? The address is the same in both main and called functions.

StructA doubleArray(int* alist, int b) {

    StructA doubled;
    int temp[b];
    for(int i=0; i < b; i++){
        temp[i] = 2 * alist[i];
    }
    doubled.a = temp;
    doubled.b = b;
    return doubled;
}

int main() {

    int arange[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    int len = 10;
    StructA hasDoubledValues = doubleArray(arange, len);
    printf("\nvalues in main :");
    for(int k = 0; k < hasDoubledValues.b; k++){
        printf(" %d  \n", hasDoubledValues.a[k]);
    }
    return 0;
}

its printing values as : 0 0 -14334592 32507 8 10 12 14 16 18 I expected the values to be : 0 2 4 6 8 10 12 14 16 18

@xing thank you. That worked properly

Benoy John
– Benoy John

2019-04-08 17:32:57 +00:00
Commented Apr 8, 2019 at 17:32 — Benoy John
– Benoy John, Commented Apr 8, 2019 at 17:32

Mohit Jain · Accepted Answer · 2019-04-07 12:42:42Z

1

int temp[b]; is local to the function. Once you return from the function, lifetime of that memory ceases and accessing it would yield undefined behaviour.

answered Apr 7, 2019 at 12:42

Mohit Jain

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