What is the problem with this code of this C to multiply digits and finding out how many times it repeats until the final number is a single digit

Question

I'm having trouble getting the outcome. The current program I wrote is to multiply each digit to get the next number and the next until the number becomes a single digit.

For example,

77 - 49 - 36 - 18 - 8 : repeats 4 times
679 - 378 - 168 - 48 - 32 - 6 : repeats 5 times

The problem with my code is that the result doesn't come out after numbers that process %d times\n

I'm guessing that the output() is the probelem.. but I'm really stuck on finding the error.

#include <stdio.h>
#pragma warning (disable : 4996)

void inputUInt(int*, int*, int*);
void myFlush();
int transNumber(int);
void output(int, int, int);

int main()
{
    int start, end, gNum;   // start number, end number, how many times until the number becomes a single digit
    inputUInt(&start, &end, &gNum);
    output(start, end, gNum);

    return 0;
}

void inputUInt(int* startp, int* endp, int* gNump)
{
    while (1) {
        printf("#start number : ");
        scanf("%d", startp);
        if (*startp >= 100 && getchar() == '\n') {
            break;
        }
        else { ; }
        myFlush();
    }

    while (1) {
        printf("#last number : ");
        scanf("%d", endp);
        if (*endp <= 10000 && *endp > * startp && getchar() == '\n') {
            break;
        }
        else { ; }
        myFlush();
    }

    while (1) {
        printf("# gNum : ");
        scanf("%d", gNump);
        if (*gNump > 0 && *gNump <= 10 && getchar() == '\n') {
            break;
        }
        else { ; }
        myFlush();
    }

    return;
}

void myFlush()
{
    while (getchar() != '\n') {
        ;
    }
    return;
}

int transNumber(int num)
{
    if (num >= 1000) {
        num = (num / 1000) * ((num % 1000) / 100) * ((num % 100) / 10) * ((num % 10) / 1);
    }
    else if (num >= 100) {
        num = (num / 100) * ((num % 100) / 10) * ((num % 10) / 1);
    }
    else if (num >= 10) {
        num = (num / 10) * ((num % 10) / 1);
    }
    else { ; }
    return num;
}

void output(int start, int end, int gNum)
{
    int i, num, transN, count = 0, gNumTotal = 0;
    printf("numbers that process %d times\n", gNum);
    for (i = start; i <= end; i++) {
        num = i;
        transN = transNumber(num);
        while (transN > 10) {
            count++;
        }
    }
    if (count == gNum) {
        printf("%d\n", i);
        gNumTotal++;
    }
    else { ; }
    printf("total numbers : %d numbers", gNumTotal);
    return;
}

Answer 1

You have to call transNumber() repeatedly in the loop. Otherwise, transN never changes, so the loop never ends.

The code that prints i needs to be inside the for loop, and you need to reset count back to 0 before each while loop.

for (i = start; i <= end; i++) {
    num = i;
    count = 0;
    while (num > 10) {
        num = transNumber(num);
        count++;
    }
    if (count == gNum) {
        printf("%d\n", i);
        gNumTotal++;
    }
}

You don't need:

else { ; }

after each if. If you don't need to do anything when the condition is false, just leave it out.