Printing an integer in english

Question

I am writing a code to display the digits of any positive integer in C language. For example, integer 345 would displayed as three four five.

The code I wrote works fine for integers with all digits greater than 0. But certain integers like 10, 304, 0 etc don't get displayed correctly. Usage of recursion and array is not allowed for the sake of challenge. Only looping and if constructs are allowed. Any suggestions?

#include<stdio.h>
int main(void)
{
    int num, num_copy, accum = 1;

    printf("Enter an integer ");
    scanf("%i",&num);

    num_copy = num;

    while (num > 0){

    while (num > 9){
        num = num / 10;
        accum *= 10;
        }
        switch (num){

        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_copy = num_copy - (num*accum);
        num = num_copy;
        accum = 1;
    }

    return 0;
}

Answer 1

Ohh! This sounds like fun! No arrays and no recursion right?

So since we can't use recursion we need to build the number backwards:

#include<stdio.h>
int main(void)
{
    int num, backwards = 0, digit, backupzeros = 0;

    printf("Enter an integer ");
    scanf("%i",&num);            // get the number

    while(num > 0){
        digit = num % 10;    // pry off the last digit
        num /= 10;           // take off the digit

        if((backwards == 0) && (digit == 0))    // If it's a number that ends in 0
            backupzeros++;                   // save it, we'll use that later

        backwards = (backwards * 10) + digit; // glue it on backwards
    }

    // Now we have the number reversed. Next we need to print the digits

    while (backwards > 0){
        digit = backwards % 10;
        backwards /= 10;

        switch (digit){

        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;
        default:
                printf("zero ");
                break;
        }
    }

    while(backupzeros > 0) {
        printf("zero ");
        backupzeros--;
    }

    return 0;
}

Answer 2

If you write a recursive function, it would help you avoid the loops that you use to print in the reverse order:

#include<stdio.h>

void print_num(int num)
{
if(num == 0) return;
print_num(num/10);

        switch (num%10){

        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;
        case (0):
                printf("zero ");
                break;
        }
}


int main(void)
{
    int num, num_copy, accum = 1;

    printf("Enter an integer ");
    scanf("%i",&num);
    print_num(num);

    return 0;
}

Non-recursive solution which uses an array to store the numbers:

void print_num(int num)
{
int i=0,j;
int arr[256];

while(num)
{
arr[i++]=num%10;
num/=10;
}

for(j=i-1; j>=0;j--)
{
        switch (arr[j]){

        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;
        case (0):
                printf("zero ");
                break;
        }
}