first occurrence code binary search debug in c

Question

int firstOcc(int a[],int m,int x)
{
    int high=m-1,low=0,mid,index=-1;

    while(low<=high){
    mid=(low+high)/2;

    if(a[mid]<x){
        mid=low+1;}

    if(a[mid]>x){
        mid=high-1;}

    if(a[mid]==x){
        index=mid;
        high=mid-1;}
    }

    return index;
}

why is my function isn't working ?! finding first occurrence. what is wrong with it ?

can't find the bug, copied almost identical code from the internet it worked but I need to know why my code isn't working

Please read [Under what circumstances may I add "urgent" or other similar phrases to my question, in order to obtain faster answers?](https://meta.stackoverflow.com/q/326569/11082165) — Brian61354270, Feb 23 '23 at 15:55
There are multiple bugs here. First, you should never change `mid` in a given iteration after setting it at the top of the loop. Instead, you need to set `low` or `high`. The assignments to `mid` after the first are dead code, since it is redefined at the top of each loop iteration. Second, you really should use `else if` and `else`. Otherwise you're doing unnecessary work. — Tom Karzes, Feb 23 '23 at 15:58
Is your input in sorted order? That's a precondition for using binary search. — John Bollinger, Feb 23 '23 at 16:06
Do apply conventional indentation to your code. That would make it far easier to read, probably even for you, yourself. — John Bollinger, Feb 23 '23 at 16:08

score 0 · Accepted Answer · answered Feb 23 '23 at 16:22

0

wrong:

        mid=low+1;}
…
        mid=high-1;}

right:

        low=mid+1;}
…
        high=mid-1;}

mid change is off the table.

answered Feb 23 '23 at 16:22

Armali

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first occurrence code binary search debug in c

1 Answers1