I am testing by using ./generate 1000 50 | ./find 127. The needle should be found but isn't.

#include <stdio.h>   
#include <cs50.h>
#include <string.h>
#include "helpers.h"

 * Returns true if value is in array of n values, else false.
bool search(int value, int values[], int n)
    if (n<1)
        return false;
    // TODO: implement a detecting algorithm, if found end loop
    int max=n-1;
    int min=0;
    while ((max-min)>0)
        int mid = ((min+max)/2);
        if (values[mid]==value)
            return true;
        if (values[mid]<value)
            min = mid+1;
        if (values[mid]>value)
            max = mid-1;               
    return false; //if not found, return false   

2 Answers 2


If i'm not wrong, your implementation fails to reach the base case. If you have the list {1,3,5} and are triyng to find 5, for example, your algorithm will do this:

max = 2;
min = 0;
max-min = 2, greater than 0, so
    mid = 1
        values[1]  < value, so
            min = 2

at this point, the condition for your while loop is reached, 2-2=0, so it will not iterate again, failing to check if values[2] == value.

  • Hmm I just corrected 'while ((max-min)>0)' to be 'while ((max-min)>=0)' but it is still not finding the needle.
    – noggy
    Oct 30, 2015 at 22:44

Perhaps it would work if you simply changed the condition of the while loop from:

while ((max-min)>0)


while (min <= max + 1)

I copied your code, made the change, tested it out, and it found the needle with no problem.

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