20.c

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

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

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

    while(n != 0)
    {
        num = (num * 10) + (n % 10);
        n /= 10;
    }
    
    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;
    }
    
    
    while(digits)
    {
        printf("Zero ");
        digits--;
    }
    
    return 0;
}