How can I put a user input value into strncpy?

Question

So, I am trying to write an strncpy function. I want user to input the number of characters to be copied from source. I am doing something wrong, but I can't understand what. This is what I tried to do:

#include <stdio.h>
#include <string.h>
#define ARR_SIZE 20

int main() {
    char string[ARR_SIZE];
    int n, m;
    char s1[4], s2[4], nstr[m];
    printf("Enter the string:");
    gets(string);
    printf("The length of the string is: %ld\n", strlen(string));

    strcpy(s1, s2);
    printf("The original string is: %s\n", string);
    printf("The copy of the original string is: %s\n", string);
    
    printf("How many characters do you want to take from this string to create another string? Enter: \n");
    scanf("%d", &n);
    strncpy(nstr, s1, m);
    printf("%s\n", nstr);
}

(On top I tried some strlen and strcpy functions.) EDIT: I totally forgot to write what was the problem. Problem is I can't get the new string which is named nstr in my code. Even though I printed it out.

Answer 1

first of all, the whole code is just a bad practice.

Anyway, here is my take on your code which copies n characters of an input string to string_copy

#include <stdio.h>
#include <string.h>
#define ARR_SIZE 20

int main() {
    char string[ARR_SIZE];
    int n;
    printf("Enter the string:");
    gets(string);
    printf("The length of the string is: %ld\n", strlen(string));

    printf("The original string is: %s\n", string);

    printf("How many characters do you want to take from this string to 
    create another string? Enter: \n");
    scanf("%d", &n);
    if(n > strlen(string)){
        n = strlen(string);
        printf("you are allowed to copy maximum of string length %d\n", n);
    }

    char string_copy[n];
    strncpy(string_copy, string, n);
    printf("%s\n", string_copy);
}

note that using deprecated functions such as gets() isn't safe. use scanf() or fgets() instead.

refer to why you shouldn't use gets()