Binary Search Program in C++

 Binary Search Program in C++

 program asks the user to input the number of elements and then the value of those elements. All the user entered numbers are stored in an array. The program then asks the user to input the search element (the number that needs to be searched in the list). The program searches the entered number in the list using binary search.

#include <iostream>
using namespace std;

int main()
{
	int count, i, arr[30], num, first, last, middle;
	cout<<"how many elements would you like to enter?:"; 
        cin>>count;

	for (i=0; i<count; i++)
	{
		cout<<"Enter number "<<(i+1)<<": "; 
                cin>>arr[i];
	}
	cout<<"Enter the number that you want to search:"; 
        cin>>num;
	first = 0;
	last = count-1;
	middle = (first+last)/2;
	while (first <= last)
	{
	   if(arr[middle] < num)
	   {
		first = middle + 1;

	   }
	   else if(arr[middle] == num)
	   {
		cout<<num<<" found in the array at the location "<<middle+1<<"\n"; 
                break; 
           } 
           else { 
                last = middle - 1; 
           } 
           middle = (first + last)/2; 
        } 
        if(first > last)
	{
	   cout<<num<<" not found in the array";
	}
	return 0;
}

Output:

how many elements would you like to enter?:5
Enter number 1: 12
Enter number 2: 45
Enter number 3: 8
Enter number 4: 9
Enter number 5: 100
Enter the number that you want to search:8
8 found in the array at the location 3

Program find the largest element in an array of n elements: 
#include <iostream>
using namespace std;
int main(){
   //n is the number of elements in the array
   int n, largest;
   int num[50];
   cout<<"Enter number of elements you want to enter: ";
   cin>>n;
   
   /* Loop runs from o to n, in such a way that first
    * element entered by user is stored in num[0], second 
    * in num[1] and so on. 
    */
   for(int i = 0; i < n; i++) {
      cout<<"Enter Element "<<(i+1)<< ": ";
      cin>>num[i];
   }
   // Storing first array element in "largest" variable
   largest = num[0];
   for(int i = 1;i < n; i++) {
      /* We are comparing largest variable with every element
       * of array. If there is an element which is greater than
       * largest variable value then we are copying that variable
       * to largest, this way we have the largest element copied
       * to the variable named "largest" at the end of the loop 
       *
       */
      if(largest < num[i])
         largest = num[i];
   } 
   cout<<"Largest element in array is: "<<largest;
   return 0;
}
Output:
Enter number of elements you want to enter: 5
Enter Element 1: 19
Enter Element 2: 21
Enter Element 3: 3
Enter Element 4: 89
Enter Element 5: 13
Largest element in array is: 89
Explanation:
User enters 5 which means the loop that stores the input values into the array runs 5 times, first entered value is stored in num[0], second in num[1] and so on.
The first element is assigned to the integer variable “largest”, this means that before starting of the second loop the value of largest is 19.
First Iteration of second loop: 19, which is the value of “largest” variable is compared with 21, since 21 is greater than 19, the “if” condition is true and the value of largest is now 21.
Second Iteration of loop: 21 (the value of largest) is compared with 3, since three is less than 21, nothing happens as the “if” condition is false.
Third Iteration of loop: 21 is compared with 89, 89 is greater than 21, “if” condition is true, the value of 89 is assigned to the “largest” variable.
Fourth Iteration of loop: 89(value of largest variable) is compared with 13, 13 is small so nothing happens.
Loop ended.
The value in “largest” variable is 89 at the end of loop, which we have displayed as the answer.