(using if, if-else, nested if, switch-case)

(using for, while, do-while loops)

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Product of digits of a number

Introduction

The product of digits of a number is obtained by multiplying all its digits together.

Example:

Input: 123 → Output: 6 (1 × 2 × 3 = 6)
Input: 405 → Output: 0 (4 × 0 × 5 = 0)

We’ll use a for, while and do..while loop to extract digits and multiply them.

C Program: Product of digits of a number

Method 1: Using for loop

#include <stdio.h>
 
int main() {
    int num, original, digit;
    long long product = 1;
 
    // Input
    printf("Enter a positive integer: ");
    scanf("%d", &num);
 
    // Validate input
    if (num < 0) {
        printf("Invalid input! Please enter a positive number.\n");
        return 1;
    }
 
    original = num; // store original number
 
    // Handle 0 as a special case
    if (num == 0) {
        product = 0;
    } else {
        // Product of digits using for loop
        for (; num != 0; num /= 10) {
            digit = num % 10;   // extract last digit
            product *= digit;   // multiply
        }
    }
 
    // Display result
    printf("Product of digits of %d = %lld\n", original, product);
 
    return 0;
}

Output

 
OUTPUT 1 :
Enter a positive integer: 123
Product of digits of 123 = 6

OUTPUT 2 :
Enter a positive integer: 405
Product of digits of 405 = 0

OUTPUT 3 :
Enter a positive integer: 0
Product of digits of 0 = 0

Explanation

Read the positive number num and store it in original.
Validate that the number is positive.
Handle 0 as a special case (product = 0).
Use a for loop:
- Extract last digit using digit = num % 10.
- Multiply it with product.
- Remove the last digit using num /= 10.
Print the final product of digits.

C Program: Product of digits of a number

Method 2: Using while loop

#include <stdio.h>
 
int main() {
    int num, original, digit;
    long long product = 1;
 
    // Input
    printf("Enter a positive integer: ");
    scanf("%d", &num);
 
    // Validate input
    if (num < 0) {
        printf("Invalid input! Please enter a positive number.\n");
        return 1;
    }
 
    original = num; // store original number
 
    // Handle 0 as a special case
    if (num == 0) {
        product = 0;
    } else {
        // Product of digits using while loop
        while (num != 0) {
            digit = num % 10;   // extract last digit
            product *= digit;   // multiply
            num /= 10;          // remove last digit
        }
    }
 
    // Display result
    printf("Product of digits of %d = %lld\n", original, product);
 
    return 0;
}

Output

 
OUTPUT 1 :
Enter a positive integer: 123
Product of digits of 123 = 6

OUTPUT 2 :
Enter a positive integer: 405
Product of digits of 405 = 0

OUTPUT 3 :
Enter a positive integer: 0
Product of digits of 0 = 0

Explanation

Read the positive number num and store it in original.
Validate that num is positive.
Handle 0 as a special case (product = 0).
Use a while loop:
- Extract last digit using digit = num % 10.
- Multiply it with product.
- Remove the last digit using num /= 10.
Print the final product.

C Program: Product of digits of a number

Method 3: Using do..while loop

#include <stdio.h>
 
int main() {
    int num, original, digit;
    long long product = 1;
 
    // Input
    printf("Enter a positive integer: ");
    scanf("%d", &num);
 
    // Validate input
    if (num < 0) {
        printf("Invalid input! Please enter a positive number.\n");
        return 1;
    }
 
    original = num; // store original number
 
    // Handle 0 as a special case
    if (num == 0) {
        product = 0;
    } else {
        // Product of digits using do-while loop
        do {
            digit = num % 10;   // extract last digit
            product *= digit;   // multiply
            num /= 10;          // remove last digit
        } while (num != 0);
    }
 
    // Display result
    printf("Product of digits of %d = %lld\n", original, product);
 
    return 0;
}

Output

 
OUTPUT 1 :
Enter a positive integer: 123
Product of digits of 123 = 6

OUTPUT 2 :
Enter a positive integer: 405
Product of digits of 405 = 0

OUTPUT 3 :
Enter a positive integer: 0
Product of digits of 0 = 0

Explanation

Read the positive number num and store it in original.
Validate that the number is non-negative.
Handle 0 as a special case (product = 0).
Use a do-while loop:
- Extract the last digit using digit = num % 10.
- Multiply it with product.
- Remove the last digit using num /= 10.
Print the final product.

Basics of C Programming (Introductory Programs)

Control Statements & Loops in C

Functions

Arrays

Strings

Pointers

Structures and Unions

Dynamic Memory Allocation

File Handling

Data Structures in C

Advanced C Programs

User-Defined Number Programs in C

User-Defined String Programs in C

C Programs

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Loop Programs in C

Product of digits of a number

Introduction

C Program: Product of digits of a number

Method 1: Using for loop

Output

Explanation

C Program: Product of digits of a number

Method 2: Using while loop

Output

Explanation

C Program: Product of digits of a number

Method 3: Using do..while loop

Output

Explanation