Array b are equal to the sum the digit of the array element a

I need help solving this problem, if anyone had a similar problem it would help me.

The task is: Write a program that loads a array a of n natural numbers and then forms a array b so that the elements of the array b are equal to the sum the digit of the array element a.

Example:
n=5
a[0]=1
a[1]=2
a[2]=3
a[3]=32
a[4]=54
Array b is:
b[0]=1
b[1]=2
b[2]=3
b[3]=5
b[4]=9

I did like this:

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

#define MAX 100

void form(int [], int [], int);
int sum_digit(int);
void print (int [], int);

int main() {
    int n;
    printf("Enter n:");
    scanf("%d", &n);
    while (n < 1 || n > MAX) {
        int n;
        printf("Enter n:");
        scanf("%d", &n);
    }
    int a[MAX], b[MAX];
    printf("Enter element of array a:\n");
    for (int i = 0; i < n; i++) {
        printf("%d. element:",i + 1);
        scanf("%d", &a[i]);
    }
    form(a, b, n);
    print(b, n);
    return 0;
}

void form(int a[MAX], int b[MAX], int n) {
    for (int i = 0; i < n; i++) {
        while (a[i] > 0) {
            int pom = a[i] % 10;
            b[i] = sum_digit(pom);
            a[i] = a[i] / 10;
        }
    }
}

int sum_digit(int s) {
    int sum = 0;
    sum = sum + s;
    return sum;
}

void print(int b[MAX], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d ", b[i]);
    }
}

The problem arises for multi-digit array elements.
Each time the sum_digit function is called the sum is set to zero.
So for example for element 32, I can’t get 5 because I can’t add 2 and 3. If anyone has an idea how to solve this I would be grateful.

Thanks in advance!

>Solution :

There are multiple problems in your code:

• you do not test the return value of scanf() so any invalid or missing input will cause undefined behavior because the destination variables will not be updated.

• There is a new variable n defined in the while loop, so the original variable in the outer scope is never modified by scanf().

• form and sum_digit are both incorrect: you should compute the sum in sum_digit() with a loop and store all sums in a loop in form.

Here is a modified version:

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

#define MAX 100

void form(int [], int [], int);
int sum_digits(int);
void print (int [], int);

int main() {
    int n;
    
    for (;;) {
        printf("Enter n:");
        if (scanf("%d", &n) != 1)
            return 1;
        if (n >= 1 && n <= MAX)
            break;
        printf("Incorrect value: %d\n", n);
    }
    int a[MAX], b[MAX];
    printf("Enter elements of array a:\n");
    for (int i = 0; i < n; i++) {
        printf("%d. element:", i + 1);
        if (scanf("%d", &a[i]) != 1)
            return 1;
    }
    form(a, b, n);
    print(b, n);
    return 0;
}

void form(int a[MAX], int b[MAX], int n) {
    for (int i = 0; i < n; i++) {
        b[i] = sum_digits(a[i]);
    }
}

int sum_digits(int s) {
    int sum = 0;
    while (s >= 10) {
        sum = sum + s % 10;
        s = s / 10;
    }
    return sum + s;
}

void print(int b[MAX], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d ", b[i]);
    }
    printf("\n");
}