I am going round and round in circles with this pset, please can someone give me some direction, below is a copy of my code:

 * helpers.c
 * Helper functions for Problem Set 3.

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

 * Returns true if value is in array of n values, else false.
bool search(int value, int values[], int n)

// TODO: implement a searching algorithm
int low = 0;
int high = n-1;
int mid = low + ((high - low) / 2);

// while length of list is greater than two
while (n > 2)
// if middle of values is equal to value, return true
if (mid == value)
return true;

// else if middle of values is greater than value, look to the left
if (mid > value)
mid = low + ((mid-1 - low) / 2);

//else if middle of values is less than value, look to the right
if (mid < value)
mid = low + ((high - mid+1) / 2);

//else return false
return false;

// Swap function
void swap(int *a, int *b)
int temp = *a;
*a = *b;
*b = temp;

 * Sorts array of n values.
void sort(int values[], int n);

// TODO: implement an O(n^2) sorting algorithm

int current;
int swapd = n-1;

for(int i = 0; i < n-1; i++)
current = values[i];

if (current > i+1)
swap (current, i);

else //(swapd == 0);
return false;



1 Answer 1


In search, while loop should not be (n>2) (you don't change n), but something like (low<=high), meaning "as long as search interval has elements".

low + ((high - low) / 2) could be just (high + low) / 2, and calculate that within the loop, just after the while.

You compare index mid to value value, but should compare values[mid] to value.

In the two comparison paths, do not assign to mid, but change high or low to mid-1 or mid+1, respecively. As you recalculate mid at the beginning of the next loop iteration (two points above), it will be adjusted accordingly.

In sort, again you compare a value values[i] to an index i+1. Compare only values. swap function should receive pointers, like swap(&values[i],&values[i+1])

A O(n²) algorithm probably needs two nested loops.

Do not return in the loop, unless you are finished with sorting. return leaves the function.

  • Thank you for this, have made changes but coming up with two errors now, but will post separate question as will need to show code again
    – Sofia
    Jan 25, 2017 at 18:04

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