C program to print number in words

Write a C program to input a number from user and print it into words using for loop. How to display number in words using loop in C programming. Logic to print number in words in C programming.

Input number: 1234

One Two Three Four

Required knowledge

Basic C programming, Switch case, While loop

Logic of convert number in words

Step by step descriptive logic to convert number in words.

1. Input number from user. Store it in some variable say num.
2. Extract last digit of given number by performing modulo division by 10. Store the result in a variable say digit = num % 10.
3. Switch the value of digit found above. Since there are 10 possible values of digit i.e. 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 hence, write 10 cases. Print corresponding word for each case.
4. Remove last digit from num by dividing it by 10 i.e. num = num / 10.
5. Repeat step 2 to 4 till number becomes 0.

The above logic is correct however it print the words in reverse order. For example, suppose number is 1234, if you apply above logic the output printed is – “Four Three Two One” instead of “One Two Three Four”. To overcome this, you must reverse the number.

Program to print number in words

/**
 * C program to print number in words
 */

#include <stdio.h>

int main()
{
    int n, num = 0;

    /* Input number from user */
    printf("Enter any number to print in words: ");
    scanf("%d", &n);

    /* Store reverse of n in num */
    while(n != 0)
    {
        num = (num * 10) + (n % 10);
        n /= 10;
    }

    /* 
     * Extract last digit of number and print corresponding digit in words
     * till num becomes 0
     */
    while(num != 0)
    {
        switch(num % 10)
        {
            case 0: 
                printf("Zero ");
                break;
            case 1: 
                printf("One ");
                break;
            case 2: 
                printf("Two ");
                break;
            case 3: 
                printf("Three ");
                break;
            case 4: 
                printf("Four ");
                break;
            case 5: 
                printf("Five ");
                break;
            case 6: 
                printf("Six ");
                break;
            case 7: 
                printf("Seven ");
                break;
            case 8: 
                printf("Eight ");
                break;
            case 9: 
                printf("Nine ");
                break;
        }
        
        num = num / 10;
    }

    return 0;
}

Update: As observed by one of our readers, the above programs fails to show correct output for any integer that ends with 0. Such as 1000, 1090, 10 etc. Therefore I have made little changes in the above program to remove the bug. I have also commented the program well enough so that it could be easy to get the logic.

Program to display number in words

/**
 * C program to display number in words
 */

#include <stdio.h>
#include <math.h>

int main()
{
    int n, num = 0, digits;

    /* Input number from user */
    printf("Enter any number to print in words: ");
    scanf("%d", &n);
    
    /* Find total digits in n */
    digits = (int) log10(n); 

    /* Store reverse of n in num */
    while(n != 0)
    {
        num = (num * 10) + (n % 10);
        n /= 10;
    }
    
    /* Find total trailing zeros */
    digits =  digits - ((int) log10(num));  

    /* 
     * Extract last digit of number and print corresponding number in words 
     * till num becomes 0
     */
    while(num != 0)
    {
        switch(num % 10)
        {
            case 0: 
                printf("Zero ");
                break;
            case 1: 
                printf("One ");
                break;
            case 2: 
                printf("Two ");
                break;
            case 3: 
                printf("Three ");
                break;
            case 4: 
                printf("Four ");
                break;
            case 5: 
                printf("Five ");
                break;
            case 6: 
                printf("Six ");
                break;
            case 7: 
                printf("Seven ");
                break;
            case 8: 
                printf("Eight ");
                break;
            case 9: 
                printf("Nine ");
                break;
        }
        
        num /= 10;
    }
    
    /* Print all trailing zeros */
    while(digits)
    {
        printf("Zero ");
        digits--;
    }
    
    return 0;
}

Enter any number to print in words: 1007
One Zero Zero Seven

Happy coding 😉