Print multiples of Unit Digit of Given Number in C Program

In C programming, finding multiples of the unit digit of a given number involves extracting the last digit and then finding all numbers that divide it evenly. The unit digit of any number can be obtained using the modulo operator (%) with 10.

Syntax

int unitDigit = number % 10;

Algorithm

START
Step 1 ? Declare variables num, unitDigit and i
Step 2 ? Input number num
Step 3 ? Store num%10 in unitDigit to fetch unit digit
Step 4 ? Print unitDigit
Step 5 ? Loop for i=2 and i<=unitDigit/2 and ++i
   IF unitDigit%i==0
      Print i
   End IF
Step 6 ? End For Loop
STOP

Example

This program extracts the unit digit and finds all its proper divisors (multiples) −

#include <stdio.h>

int main() {
    int num, unitDigit, i;
    
    printf("Enter a number: ");
    scanf("%d", &num);
    
    unitDigit = num % 10;  // storing unit digit
    printf("Unit digit of %d is: %d<br>", num, unitDigit);
    
    printf("Multiples of %d are: ", unitDigit);
    
    // Special case for 0 and 1
    if (unitDigit == 0) {
        printf("All numbers are multiples of 0<br>");
    } else if (unitDigit == 1) {
        printf("1 has no proper multiples<br>");
    } else {
        // Find proper divisors (multiples) from 2 to unitDigit/2
        int found = 0;
        for (i = 2; i <= unitDigit / 2; i++) {
            if (unitDigit % i == 0) {
                printf("%d ", i);
                found = 1;
            }
        }
        if (!found) {
            printf("No proper multiples found");
        }
        printf("<br>");
    }
    
    return 0;
}

The output of the above code is −

Enter a number: 326
Unit digit of 326 is: 6
Multiples of 6 are: 2 3

How It Works

• The expression num % 10 extracts the unit digit by finding the remainder when divided by 10.
• We loop from 2 to unitDigit/2 because no number greater than half of the unit digit can divide it (except itself).
• For each number i, if unitDigit % i == 0, then i is a proper divisor (multiple).
• Special handling is added for digits 0 and 1 to avoid confusion.

Conclusion

This program demonstrates how to extract the unit digit using modulo operation and find its proper divisors efficiently. The algorithm runs in O(n/2) time where n is the unit digit value.