/*
  Third lesson in C

  We've already covered things like include <stdio.h> and printf for writing
  stuff out to the screen now we'll look at going the other way, reading
  input in from a user

  Reading data in.
*/

#include <stdio.h>

int main() {
    /*
      Before we can read anything in from the user we have to declare a couple
      of variables so we'll have somewhere to put what we read in.

      You almost always do this at the begining of a function or at the beginning
      of the program (or in .h files just to complicate it but that's a lesson for
      later)

      The first variable will be "line" and will be big enough to hold 50 char (a
      really small string)
    */
    char line[50];
    /*
      To break that down

      char is the type (remember when I explained the "int" in the "int main() {"
      line is the variable name (like "main" is the function name)
      [50] says to make a variable big enough to hold 50 of whatever the type is

      This line variable will be used for reading in from the console, now we need
      a variable to store an integer in.
    */
    int value;

    printf("Enter a value: ");

    /*
      fgets, like printf, is provided as part of the stdio library. This function
      reads characters from a input stream and stores them as a C string into str
      until either 1 less than the specified number of characters have been read
      in this case 50 so 49 characters will be read) or a newline or the
      end-of-file is reached, whichever happens first.

      Newlines come when users push enter, so that's what we'll aim for, a note for
      later, the new line will actually be appended to the string, it's not
      something to worry about today.
    */
    fgets(line, 50, stdin);
    /*
      Broken down:

      fgets(
        line  - store the data in the variable we declared before,
        50    - can store at most this number of characters in the variable
        stdin - read fromt he special input handle "stdin" (standard in)
      )

      Standard in for the sake of this lesson is the console you're working in
      but it can be many other things.

      So now we have data from the user sitting in line, what shall we do with it?

      Lets grab an integer from it with sscanf.
      sscanf is basically the exact oposite of sprintf which is similar to printf

      where printf prints formatted text out
      sprintf stores formatted text in a string
      sscanf reads formatted text back to variables
    */
    sscanf(line, "%d", &value);
    /*
      Broken down this one is a little more complicated than the last one

      sscanf(
        line   - scan the data stored in the line variable we filled with fgets
        '%d'   - look for a number (like the %d in printf)
        &value - store the resulting number at the address of the value variable
      )

      The complicated bit is the &value. Value is a value stored at an address,
      the & prefix causes c to pass the address of value rather than what is stored
      there (think of it as pointing to the shelf the milk is on rather than giving
      up a bottle of milk)

      So, now you have an integer stored in value that should be something you
      inputted.

      Print it back out!
    */
    printf("Your number was %d!\n", value);

    return 0;
}