In this article, you'll learn and get code about how to search an element from given array using binary search technique. But before going through the program, if you are not aware of how binary search works, then I recommend you to go through the step by step working of Binary search.
Here are the list of programs you will go through over here, with its step by step explanation:
This is the simplest program of binary search. Simplest in the sense, here we have directly asked from user to enter 10 element or numbers without giving to specify the size of array and then enter his/her required amount of element. Also the sorting code block is not included in this program. So I've just asked to enter already sorted array as input. Let's take a look at the program:
#include<stdio.h> #include<conio.h> int main() { int i, arr[10], search, first, last, middle; printf("Enter 10 elements (in ascending order): "); for(i=0; i<10; i++) scanf("%d", &arr[i]); printf("\nEnter element to be search: "); scanf("%d", &search); first = 0; last = 9; middle = (first+last)/2; while(first <= last) { if(arr[middle]<search) first = middle+1; else if(arr[middle]==search) { printf("\nThe number, %d found at Position %d", search, middle+1); break; } else last = middle-1; middle = (first+last)/2; } if(first>last) printf("\nThe number, %d is not found in given Array", search); getch(); return 0; }
This program was written under Code::Blocks IDE. Here is the initial snapshot of sample run:
Now provide any 10 elements in ascending order, say 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 and then press ENTER key. Again enter any element or number to be search say 7, press ENTER key to see the output given in the snapshot here:
If user supply all the 10 numbers as entered in above output. But this time, when he/she entered any number say 15 to be search from the given list of number, then here is the output you will see:
Here is the modified version of binary search program (as given above) in C. Here we have leave the size of array to be decided by user at run-time. And before performing the binary search, bubble sort is used to sort the given array in ascending order.
Important - This program finds the position of number from sorted array, not from the actual array that is entered by user at run-time. For example, if user supply 10, 50, 20, 30, 40 as array input, and 20 as number to be search. Then this program sort the array, so the array becomes 10, 20, 30, 40, 50 and the position of 20 will be 2.
#include<stdio.h> #include<conio.h> int main() { int i, j, n, arr[100], search, first, last, middle, temp; printf("How many element you want to store in array ? "); scanf("%d", &n); printf("\nEnter %d array elements: ", n); for(i=0; i<n; i++) scanf("%d", &arr[i]); printf("\nEnter element to be search: "); scanf("%d", &search); // sorting given array using bubble sort for(i=0; i<(n-1); i++) { for(j=0; j<(n-i-1); j++) { if(arr[j]>arr[j+1]) { temp = arr[j]; arr[j] = arr[j+1]; arr[j+1] = temp; } } } // sort array printf("\nNow the sorted Array is:\n"); for(i=0; i<n; i++) printf("%d ", arr[i]); // back to binary search first = 0; last = n-1; middle = (first+last)/2; while(first <= last) { if(arr[middle]<search) first = middle+1; else if(arr[middle]==search) { printf("\n\nThe number, %d found at Position %d", search, middle+1); break; } else last = middle-1; middle = (first+last)/2; } if(first>last) printf("\nThe number, %d is not found in given Array", search); getch(); return 0; }
Here is the snapshot of sample run:
Now modify the first program of this article that does the same job but this time using function as shown in the program given below:
#include<stdio.h> #include<conio.h> int binarySearchFun(int arr[], int); int main() { int i, arr[10], search, pos; printf("Enter 10 elements (in ascending order): "); for(i=0; i<10; i++) scanf("%d", &arr[i]); printf("\nEnter element to be search: "); scanf("%d", &search); pos = binarySearchFun(arr, search); if(pos==0) printf("\nThe number, %d is not found in given Array", search); else printf("\nThe number, %d found at Position %d", search, pos); getch(); return 0; } int binarySearchFun(int arr[], int search) { int first, last, middle; first = 0; last = 9; middle = (first+last)/2; while(first <= last) { if(arr[middle]<search) first = middle+1; else if(arr[middle]==search) { return (middle+1); } else last = middle-1; middle = (first+last)/2; } return 0; }
This is the snapshot of sample output produced after running the above program:
To learn more about function, refer to Function in C tutorial.
This is the last program on binary search. This program used recursive function to find the number from the given array using binary search technique. Let's take a look at the program:
#include<stdio.h> #include<conio.h> int binarySearchRecFun(int [], int, int, int); int main() { int i, arr[10], search, pos; printf("Enter 10 elements (in ascending order): "); for(i=0; i<10; i++) scanf("%d", &arr[i]); printf("\nEnter element to be search: "); scanf("%d", &search); pos = binarySearchRecFun(arr, 0, 9, search); if(pos==0) printf("\nThe number, %d is not found in given Array", search); else printf("\nThe number, %d found at Position %d", search, pos); getch(); return 0; } int binarySearchRecFun(int arr[], int first, int last, int search) { int middle; if(first>last) return 0; middle = (first+last)/2; if(arr[middle]==search) return (middle+1); else if(arr[middle]>search) binarySearchRecFun(arr, first, middle-1, search); else if(arr[middle]<search) binarySearchRecFun(arr, middle+1, last, search); }
You will get the same output as shown in the output of above program, that is, binary search using function. To learn more about recursion, refer to Recursion in C tutorial.
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