Binary search accessing out of range index

Question

This is the code:

char binarySearch(unsigned int target, int* primes, unsigned int size){
    int* ptrToArray = primes;
    unsigned int first = 0;
    unsigned int last = size;

    while (first <= last){
        unsigned int middle = first + (last - first) / 2;
        printf("first: %d, last: %d, middle: %d\n", first, last , middle);

        if (ptrToArray[middle] == target){
            return 1;
        }

        if (ptrToArray[middle] < target){
            first = middle + 1;
        }else{
            last = middle - 1;
        }
    }
    return 0;
}

This is the output:

I've been staring at that peace of code for more than one should and still can't figure out where is the flaw.

Answer 1

If middle is 0, as near the end of your debug output, the statement

last = middle - 1

causes an integer overflow; the conditions have to be reworked a bit.