Problem Statement & Approach

Given an integer n, compute the sum of all its individual digits. For example, for $n = 4832$, the sum of digits is $4 + 8 + 3 + 2 = 17$.

Extraction Logic:

1. Extract the last digit: lastDigit = n % 10
2. Add to sum: sum += lastDigit
3. Remove the last digit: n = n / 10
4. Repeat until n == 0.

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C Code Implementation

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>
#include <stdlib.h>

int sumOfDigitsIterative(int n) {
    n = abs(n); /* Handle negative inputs */
    int sum = 0;

    while (n > 0) {
        sum += n % 10;
        n /= 10;
    }
    return sum;
}

int sumOfDigitsRecursive(int n) {
    n = abs(n);
    if (n == 0) {
        return 0;
    }
    return (n % 10) + sumOfDigitsRecursive(n / 10);
}

int main() {
    int testValues[] = {4832, 9999, -512, 0, 7};
    int len = sizeof(testValues) / sizeof(testValues[0]);

    for (int i = 0; i < len; i++) {
        int val = testValues[i];
        printf("Sum of digits for %d:\n", val);
        printf("  Iterative: %d\n", sumOfDigitsIterative(val));
        printf("  Recursive: %d\n\n", sumOfDigitsRecursive(val));
    }

    return 0;
}

Sample Output

text (ISO Standard)
Copy
Sum of digits for 4832:
  Iterative: 17
  Recursive: 17

Sum of digits for 9999:
  Iterative: 36
  Recursive: 36

Sum of digits for -512:
  Iterative: 8
  Recursive: 8

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Complexity Analysis

• Time Complexity: O(log₁₀ n) — We process each digit exactly once.
• Space Complexity: O(1) iterative, O(log₁₀ n) stack frames recursive.

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Related Guides

• Check if digits read the same backwards in Palindrome Program in C.
• Master loops in C Programming Basics.