C++ Program to Find Sum of First and Last Digit of a Number

This article is created to provide some programs in C++ to find and print the sum of first and last digit of a given number. The program is created in following ways:

  • Using while loop
  • Using for loop
  • Using user-defined function

Find Sum of First and Last Digit using while Loop

The question is, write a program in C++ that receives a number from user as input and print the sum of first and last digit of given number as output. Here is its answer:

#include<iostream>

using namespace std;
int main()
{
   int num, temp=0, last, rem, sum=0;
   cout<<"Enter a Number: ";
   cin>>num;
   while(num!=0)
   {
      if(temp==0)
      {
         last = num%10;
         temp++;
      }
      rem = num%10;
      num = num/10;
   }
   sum = rem + last;
   cout<<"\nSum of First ("<<rem<<") and Last ("<<last<<") Digit = "<<sum;
   cout<<endl;
   return 0;
}

The snapshot given below shows the initial output produced by above C++ program on finding the sum of first and last digit of given number:

c++ find sum of first and last digit of number

Now supply the number say 23094 as input and press ENTER key to find and print the sum of first (that is 2) and last (that is 4) digit of this number like shown in the snapshot given below:

find sum of first and last digit c++

In above program, the dry run of following block of code:

   while(num!=0)
   {
      if(temp==0)
      {
         last = num%10;
         temp++;
      }
      rem = num%10;
      num = num/10;
   }

with num=23094, temp=0, sum=0 goes like:

  • The condition num!=0 or 23094!=0 evaluates to be True
  • Therefore program flow goes inside the loop and the condition of if gets evaluated
  • That is, the condition temp==0 or 0==0 evaluates to be True
  • Therefore program flow goes in the body of if and num%10 or 23094%10 or 4 gets initialized to last
  • And the value of temp gets incremented. So temp=1. Because the value of temp is 1 from now, therefore the condition of if always gets evaluated to be False from now
  • This means, the variable last holds 4 as its final value. That is the last digit of given number
  • Now after exiting from the if, num%10 or 23094%10 or 4 gets initialized to rem. This statement is created to get the last remainder, that is 2 at last execution
  • And the last statement of the loop gets executed, that is num/10 or 23094/10 or 2309 gets initialized to num. Therefore num=2309 now
  • Since all statements available in the body of while loop gets executed, therefore program flow evaluates its condition again
  • That is, the condition num!=0 or 2309!=0 again evaluates to be True. Therefore program flow again goes inside the loop
  • This process continues, until the condition evaluates to be False
  • In this way, after exiting from the loop, we will have last=4 and rem=2
  • Therefore just add them and print the addition result of first and last digit of given number. That's it

Find Sum of First and Last Digit using for Loop

Since for loop also contains initialize and update statements along with condition checking. Therefore, just place any initialization say temp=0 or sum=0 and the update statement as num = num/10 like shown in the program given below:

#include<iostream>

using namespace std;
int main()
{
   int num, temp, last, rem, sum=0;
   cout<<"Enter a Number: ";
   cin>>num;
   for(temp=0; num!=0; num=num/10)
   {
      if(temp==0)
      {
         last = num%10;
         temp++;
      }
      rem = num%10;
   }
   sum = rem + last;
   cout<<"\nSum of First ("<<rem<<") and Last ("<<last<<") Digit = "<<sum;
   cout<<endl;
   return 0;
}

This program exactly produces same output as of previous program.

Find Sum of First and Last Digit using Function

This is the last program of this article, created using a user defined function named sumfun() that takes the given number as its argument and returns the sum of first and last digit of its argument.

#include<iostream>
using namespace std;

int sumfun(int);
int main()
{
   int num, sum;
   cout<<"Enter a Number: ";
   cin>>num;
   sum = sumfun(num);
   cout<<"\nSum of First and Last Digit = "<<sum;
   cout<<endl;
   return 0;
}
int sumfun(int n)
{
   int t=0, l, r, s=0;
   while(n!=0)
   {
      if(t==0)
      {
         l = n%10;
         t++;
      }
      r = n%10;
      n = n/10;
   }
   s = r + l;
   return s;
}

Here is its sample run with user input 12030:

find sum of first last digit using function c++

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