Why does my binary search only work with if statements in this order?

Question

I'm wondering why my binary search code doesn't work with this code (it returns everything as found):

int BinarySearch(int arr[], int len, int target) {
    int first = 0;
    int last = len-1;
    int mid = (first+last)/2;
    while (first <= last) {
        mid = floor((first+last)/2);            
        if (target = arr[mid]) {
            return 1;
        } else if (target < arr[mid]) {
            last = mid-1;
        } else {
            first = mid+1;
        }
    }
    return -1;
}

But the following works. The only difference is the order of if statements in the while loop.

int BinarySearch(int arr[], int len, int target) {
    int first = 0;
    int last = len-1;
    int mid = (first+last)/2;
    while (first <= last) {
        mid = floor((first+last)/2);            
        if (arr[mid] < target) {
            first = mid+1;
        } else if (target = arr[mid]) {
            return 1;
        } 
        else { //arr[mid] < target
            last = mid-1;
        }           
    }
    return -1;
}

Answer 1

if (target = arr[mid]) 

This is an assignment , not just a comparison. It will make target be equal to arr[mid] (and then enter the block, unless the value is 0 ).

Answer 2

if (target = arr[mid]) { really? Do you mean == ?

Just in addition to the answers mentioned, the = operator assigns and then returns the value assigned if the assignment was successful. For eg. if you do printf("%d", (a = 10)); you will see 10 printed. So, when you use the assignment operator in a if statement, it boils down to something like if (10) (or some other number) and thus your if block gets executed. I hope it is obvious why if (a = 0) wont get you to execute the if block. HTH.

Answer 3

if (target = arr[mid]) 

this is wrong as it assigns a value to target and apparently you want to compare, so do this

if (target == arr[mid])

use the double ==