how to return a string from function in c

Question

Im helping my friend in is HW and i got a weird blackout. I'm using a function which designated to "decrypt" a message from a given string, the process is working fine(i debugged that to check) but i forgot how to return the value from the function to the main program I have not touched in C lang for a while so im little blacked out here

Code(Edited):

    void func(char* str, char* new_str, int i, int k) {
    if (i < strlen(str)) {
        if ((str[i] >= 'a' && str[i] <= 'z' || str[i] >= 'A' && str[i] <= 'Z')) {
            new_str[k] = str[i];
            func(str, new_str, i + 1, k + 1);
        }
        else {
            func(str, new_str, i + 1, k);
        }
    }
}


int main()
{
    char str[100] = "l#e%i&n^&%a^&%D$%o#@T(r*e^^t*t(e%$L"; //Iterate from end to start.
    char new_str[100] = ""; //Use k index here.
    func(str, new_str, 0, 0);
    printf("%s", new_str);
    return 0;
}

Answer 1

You return a pointer (reference) to the first character of the string.

char* someFunction() {
  char* newString = malloc( sizeof( char ) * 13 );
  strncpy( newString, "hello world!", 12 );
  newString[12] = '\0';
  return newString;
}

If your string can't be modified (because it is hard-coded) return a const char*

const char* someFunction2() {
  return "hello world!";
}

In both of these cases, the returned value is an address, pointing to a char. The C-convention of the first '\0' character terminating the string is what is used to find the end of the string.

Answer 2

I would not make the function return anything at all

pass a pointer to it like this:

void func(char* str, char* new_str, int i, int k)

and then override new_str[] in the function. Also, remember that char[10] initializes an array of 10 chars, so if anything you must return a pointer char*, not a single char.