C Dynamic Array Size

Hello I am new to coding and was just wondering why the below code:

#include <stdio.h>

int main() {

for(int i = 0; 1 ; i++) {

    char x;
    char z[1+i];
    x=getchar();
    if (x == '\n'){
        *(z+i) = '\0';
        printf("%s",z);
        break;}
    *(z+i) = x;
    printf("%s, %d = %c, i = %d\n",z, (z+i),*(z+i),i);
}

return 0;
}

of C does not work for inputs that are more than 15 characters? (I don't think it is beacuse of the current state of my pc since I tried it with an online compiler and it still breaks at 16 chars, but then again I am new to coding.) Would appreciate any help. Thank you. (If the answer is something like: "Thats not possible in C" or something like that please don't leave it at that and explain why it is not possible).

PS: I cheked some of the similar questions to mine but I don't get what any of them are doing, if this post is a duplicate, I would really appreciate if you could link me to the post that solves my issue, I will delete this post shortly after if that is the case.

This is the input and output of my program for 16 chars,

1234567890123456
1, 6421952 = 1, i = 0
12, 6421953 = 2, i = 1
123, 6421954 = 3, i = 2
1234, 6421955 = 4, i = 3
12345, 6421956 = 5, i = 4
123456, 6421957 = 6, i = 5
1234567, 6421958 = 7, i = 6
12345678, 6421959 = 8, i = 7
123456789, 6421960 = 9, i = 8
1234567890, 6421961 = 0, i = 9
12345678901, 6421962 = 1, i = 10
123456789012, 6421963 = 2, i = 11
1234567890123, 6421964 = 3, i = 12
12345678901234, 6421965 = 4, i = 13
123456789012345, 6421966 = 5, i = 14
1234567890123456p@, 6421967 = 6, i = 15

Process returned 0 (0x0)   execution time : 4.076 s
Press any key to continue.

And this is the input and output for 15 chars,

123456789012345
1, 6421952 = 1, i = 0
12, 6421953 = 2, i = 1
123, 6421954 = 3, i = 2
1234, 6421955 = 4, i = 3
12345, 6421956 = 5, i = 4
123456, 6421957 = 6, i = 5
1234567, 6421958 = 7, i = 6
12345678, 6421959 = 8, i = 7
123456789, 6421960 = 9, i = 8
1234567890, 6421961 = 0, i = 9
12345678901, 6421962 = 1, i = 10
123456789012, 6421963 = 2, i = 11
1234567890123, 6421964 = 3, i = 12
12345678901234, 6421965 = 4, i = 13
123456789012345, 6421966 = 5, i = 14
123456789012345
Process returned 0 (0x0)   execution time : 4.150 s
Press any key to continue.

As you can see it works fine for 15 chars of input, but breaks at 16, this is the problem that I want to be solved.

I know that I didn't explain the purpose of the code but here is the final version of the code which is highly based on FuzzFoo's answer.

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

int str_input(char **y);

int main()
{
    char * y = NULL;

    str_input(&y);

    printf("%s\n", y);

    str_input(&y);

    printf("%s", y);

    free(y);

    return (0);
}

int str_input(char **y)
{
    int i;
    char x;

    for (i = 0; 1 ; i++)
    {
        x = getchar();
        *y = (char *)realloc(*y, (2 + i) * sizeof(char));

        if (*y == NULL)

            break;

        if (x == '\n')
        {
            (*y)[i] = '\0';
            break;
        }

        (*y)[i] = x;
        (*y)[i + 1] = '\0';
    }

    return (0);
}

Hopefully this version of the code isn't trying to utilize any undefined behaviour and works for (virtually) all lengths of input. Purpose of it is to make the str_input function sort of assign strings to a pointer variable.(I know it is a little more complicated than that, but it is what it is.)(And also memory is assigned dynamically so it actually works for longer inputs.)