I am trying to make a C string calculator. This means that I have a string with numbers and a delimiter in the middle. the delimiter can be of any size as long as it isn't a number. Also, if the value of a specific number is between 1001 and 1111 it cannot be used and will be ignored (set to zero). The difficulty of this assignment is to make the delimiting/splitting string part without `strtok`. I am getting all sorts of wrong outputs and I have no idea what I am doing wrong, yet I feel like I am oversighting something or doing something incredibly stupid. The code also freezes my unit tests, so I cant even test what is going wrong.

```
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <stdbool.h>

void ValidateInput(int *x) {
    if (*x >= 1001 && *x <= 1111) { 
        x = 0;
    }
}

int test(char *numbers, int numbers_length, int *result) {
    char cnum1[numbers_length];
    char cnum2[numbers_length];

    strcpy(cnum1, "");
    strcpy(cnum2, "");

    bool x = false;
    size_t i = 0;

    while (numbers[i] != '\0') {
        char c = numbers[i];
        if (isdigit(c)) {
            if (x) {
                strcat(cnum2, &c);
            }
            if (!x) {
                strcat(cnum1, &c);
            }
        }
        if (!isdigit(c)) {
            x = true;
        }
        i++;
    }

    int num1;
    num1 = atoi(cnum1);
    int num2 = atoi(cnum2);

    ValidateInput(&num1);
    ValidateInput(&num2);

    printf("%d\n", num1);
    printf("%d\n", num2);

    return num1 + num2;
}

int main() {
    int sum;
    char numbers[] = "100,10";
    int length = strlen(numbers);
    test(numbers, length, &sum);
    return -1;
}

```