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C++ Program for Sum of Digits of a Number

In this example, we will learn to find or calculate the sum of digits of the number entered by the user in the C++ program. For Example if user enter 123, then sum of digits is 1 + 2 + 3 = 6.

C++ program to find the sum of Digit by using

For loop
while loop
do while loop
using user define function
using class

Algorithm:

Take a number from the user.
Find the remainder.
Add remainder of a number
Divide n value by 10.
Repeat steps 2 to 4 until the number becomes 0.

Now let's see Sum of the digit program

Find Sum of digit using While loop


#include<iostream>
using namespace std;
int main()
{
    int n, rem, sum = 0;
    cout<<"Enter the number: ";
    cin>>n;
    while(n != 0)
    {
        rem = n % 10;
        sum = sum + rem;
        n = n / 10;
    }
    cout<<"\nSum of Digits of a number = "<<sum;
    cout<<endl;
    return 0;
}

output

Enter the number: 12
Sum of Digits of a number = 3

Explaination:

In the above program, you will take a number from the user and store it in a variable n.

Now iterate the loop until the user value i.e n becomes zero. inside loop finds the remainder of variable n and stores it in rem.

Add the remainder i.e rem into the sum variable. when the loop end print the sum of the digit.

Time complexity: O(n)

using for loop

In this example, we will find the sum of digits by using for loop. the output and time complexity of this program is the same as above.


#include<iostream>
using namespace std;
int main()
{
    int n, rem, sum;
    cout<<"Enter the number: ";
    cin>>n;
    for(sum=0; n != 0; n/=10)
    {
        rem = n % 10;
        sum = sum + rem;
    }
    cout<<"\nSum of Digits of a number = "<<sum;
    cout<<endl;
    return 0;
}

Using Do while loop

This program is the same as above only here we have uses a do-while loop for calculating sum of the digit.


#include<iostream>
using namespace std;
int main()
{
    int n, rem, sum = 0;
    cout<<"Enter the number: ";
    cin>>n;
    do
    {
        rem = n % 10;
        sum = sum + rem;
        n = n / 10;
    } while(n != 0);
    cout<<"\nSum of Digits of a number = "<<sum;
    cout<<endl;
    return 0;
}

Using user define function

In this program, we use the user defines a function for finding the Sum of digits of a number. The output will same as the above program.


#include<iostream>
using namespace std;

int SumOfDigits(int n)
{
    int sum=0, rem;
    while(n != 0)
    {
        rem = n % 10;
        sum = sum + rem;
        n = n / 10;
    }
    return sum;
}

int main()
{
    int n;
    cout<<"Enter the number: ";
    cin>>n;
    cout<<"\nSum of Digits of a number = "<<SumOfDigits(n);
    cout<<endl;
    return 0;
}

you will pass user input i.e n as an argument in the function SumOfDigits( ). It will calculate and return the sum of all digits.

Using Class

In this C++ program, we will write the sum of digits program by using Class.


#include<iostream>
using namespace std;
class studyfame
{
    private:
        int n, sum, rem;
    public:
        void getData();
        int SumOfDigits();
};
void studyfame::getData()
{
    cout<<"Enter the Number: ";
    cin>>n;
}
int studyfame::SumOfDigits()
{
    sum=0;
    while(n != 0)
    {
        rem = n % 10;
        sum = sum + rem;
        n = n / 10;
    }
    return sum;
}
int main()
{
    studyfame s;
    int sum;
    s.getData();
    sum = s.SumOfDigits();
    cout<<"\nSum of Digits of a number = "<<sum;
    cout<<endl;
    return 0;
}

output

Enter the Number: 123
Sum of Digits of a number = 6

Time complexity of all above program: O(n)

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