Binary Search Int Array Size Issue

Question

I have been trying to figure this out all day and cannot seem to make it work. Why does my binary search work if I input the array length in manually but when I swap the manual input for:

int max = sizeof(list)/sizeof(list[0]);

it doesn't seem to work. For instance if I try to search for a 2 in a 11 element array of 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 it can't find 2. But if I change int min = 11. It can find 2. Here is the function binary sort:

int binarysearch(int *list, int sfor)

    int min = 0;
    int max = 10; 
    int mid = (min + max)/2;

    while(min <= max)
    {
        if (sfor == list[mid])
        {
            printf("The number you are searching for is in %i place \n", mid + 1);
            return 0;
        }
        else if (sfor < list[mid])
        {
            max = mid - 1;
        }
        else
        {
            min = mid + 1;
        }

        mid = (min + max)/2;
    }

        printf("Could not find number! \n");
        return 1;



int main(int argc, string argv[]) // number searching for is passed through 
{                                 // command line argument

    printf("How many numbers did you want to search through? \n");
    int a = GetInt(); //int a is how big should the array of numbers be
    printf("What are they: \n");

    int i = 0;
    int b[a];

    for (i = 0; i < a; i++)
    {
        b[i] = GetInt(); //cycles though each int of the array
    }

    int x = atoi(argv[1]); //converts command line argument to an int

    binarysearch(b, x);
}

Will greatly appreciate any help.

Answer 1

Your problem is here:

int min = sizeof(list)/sizeof(list[0]); 

That will not work for arrays passed to functions (as you cannot actually pass an array to a function). You must also pass the size of the array.