C PROGRAMMING PROGRAM • LOOPS & NUMBER PROBLEMS

Find the Sum of Digits Using a Loop

Learn how to find the sum of digits using a loop using a clear C program.

Beginnerwhile loopModulusDigit sum

PROBLEM UNDERSTANDING

Input and expected output

Sample input

Sample output

Digit sum = 23

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    long long number, value;
    int sum = 0;

    printf("Enter an integer: ");
    scanf("%lld", &number);
    value = number < 0 ? -number : number;
    while (value > 0) {
        sum += (int) (value % 10);
        value /= 10;
    }
    printf("Digit sum = %d\n", sum);
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Digit sum = 23

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Add the last digit and remove it repeatedly until no digits remain.
Display the computed result.

Add the last digit and remove it repeatedly until no digits remain.

EFFICIENCY

Time and space complexity

Time complexity

O(d)

Auxiliary space

O(1)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.