Cbinsearch, C (gcc)

Cbinsearch

//gcc 7.4.0

//write a function to search for a particular item from a sorted array of integers using the binary search method; and show how this function may be used in a program(use pointer)
//code is created by Rezaul Hoque on May 31,2021
//please contact at jewelmrh@yahoo.com
//note: codes shared by Rezaul Hoque on rextester are not for sale; they are created and shared to facilitate the algorithm learning process; many like Hoque use this platform to practice programming ;Rezaul hopes his contribution helps others to fine tune their  learning;

//binary search works like this: it compares the searched key with the middle element of the sorted array; if the searched key is smaller than the middle item than first half of the array is searched otherwise the second half is searched; in all circumstances only half of the sorted items is taken into account;
#include <stdio.h>
int binSearch(int*,int,int,int);//binSearch function takes one integer pointer and three integers as parameters
//the name of the array itself is a constant pointer to the first element of the array; so it is better to make good use of the array name, the constant pointer 
int binSearch(int *a, int low, int high, int key) {
  if (high >= low) {//as long as high is greater or equal to low do the following 
    
    int mid = low + (high - low) / 2; //calculate the middle item
     
    
    if (*(a+mid) == key) return mid; // *(a+mid) is value stored in the middle item of the array; here if the searched key is equal to that value then return the middle item 
     
//if the searched key is smaller than the middle item then do binary search in the first half of the array; note in first half the high is set to mid-1, the ending point of the search
    if (*(a+mid) > key) 
      return binSearch(a, low, mid - 1, key); 
    
    //if the searched key is higher than the middle item then do binary search in the second half of the array; note in second half the low is set to mid+1, the starting point of the search

return binSearch(a, mid + 1, high, key); 
  } 
     
  
  return -1; //the searched key is not found 
}

int main()
{
  int a[] = {15, 21, 33, 44, 50, 60};
  int key = 0;

//get the key from user
  printf("Enter Search Item: ");
  scanf("%d", &key);

int size = sizeof(a)/sizeof(a[0]);//size of arrays is calculated with the aid of sizeof operator; sizeof(a) yields the number of bytes needed to store 5 integers of array a; 10 in this case; and sizeof(a[0]) gives the number of bytes needed to store first element of the array, which is 2 in this case; so, 10/2 yields 5;

//
  int found = binSearch(a, 0, size, key);//found is assigned the return values of binSearch()
  
  if(found == -1)//if the searched key is not found 
printf("%d The item is not found\n", key);

else
    printf("\n%d The item is found at %d\n", key, found);

return 0;
}


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