Question

In C++:

Write a C++ function binsearch that carries out the binary search algorithm on a sorted
array of integers. Your function takes as parameters an array of integers (sorted in
increasing order), the size of the array, and a target integer to search for. The function
returns the index of the target in the array, and returns -1 if the target is not in the array.

Using the code below, add your binsearch function to this C++ program. (Do not change the code that generates the array.).

Use your function to search for the elements {39, 47, 208, 288, 427, 685, 676, 972}. Your program should print out each of
these elements, and the return value of the function for that element, that is, the index
in the array a where the element was found, or the integer -1 if the element was not found.

#include <iostream>
# include <cstdlib>

using namespace std;

int mainone()
{
    int a[100];
    srand(300);
    for ( int k = 0; k < 100; ++k){
        a[k] = 10*k + rand()%10;
    }

}

....

Answer 1

I have implemented the above binary search program in c++.

there are 3 functions: binsearch(), mainone(), main().

Note: You may look the screenshot of the code to have better understanding of the indentation.

c++ code:

#include<iostream>
#include<cstdlib>

using namespace std;

//binary search function
int binsearch(int a[],int n,int x)
{
//low, high, middle variables
int l=0,h=n-1,m;

while(l<=h)
{
//find middle
m = (l+h)/2;
//if found
if(a[m] == x)
return m;
else if(x < a[m])
h = m-1;
else
l = m+1;
}
//not found
return -1;
}

//user function
int mainone()
{
int a[100];
srand(300);
for(int k=0;k<100;++k)
{
a[k] = 10*k + rand()%10;
}

//print the elements
for(int i=0;i<100;i++)
cout<<a[i]<<" ";

//call binary search function
int index = binsearch(a,100,39);
cout<<"\nElement 39: "<<index<<endl;
index = binsearch(a,100,47);
cout<<"Element 47: "<<index<<endl;
index = binsearch(a,100,208);
cout<<"Element 208: "<<index<<endl;
index = binsearch(a,100,288);
cout<<"Element 288: "<<index<<endl;
index = binsearch(a,100,427);
cout<<"Element 427: "<<index<<endl;
index = binsearch(a,100,685);
cout<<"Element 685: "<<index<<endl;
index = binsearch(a,100,676);
cout<<"Element 676: "<<index<<endl;
index = binsearch(a,100,972);
cout<<"Element 972: "<<index<<endl;
index = binsearch(a,100,771);
cout<<"Element 771: "<<index<<endl;
}

//main function
int main()
{
//call the function mainone
mainone();
return 0;
}
Output:

Screenshot of code: