Structures.

[omnificient]

I've got the following code:

#include <stdio.h>
struct first {
       int a;
       int b;
};
int main()
{
  struct first;
  scanf(" %d", &first.a);
  scanf(" %d", &first.b);
  getchar();
  return 0;
}

My compiler gives me a warning that the variables a and b haven't been declared. I don't really understand what mistake I have made here. Is it with the structure in general, or did I commit a mistake in the syntax?

Thank You.

[Dave_Sinkula]

struct first; is the type -- like say int;
struct first first; is a type and an object -- like int i;

[vart]

struct firt is a type
writing
struct first;

as if writing

int;

you should declare variable

struct first myVar;
myVar.a = 7;

[omnificient]

I now have:

#include <stdio.h>
struct first {
       int a;
       int b;
};
int main()
{
  struct first var;
  scanf(" %d", &var.a);
  scanf(" %d", &var.b);
  getchar();
  return 0;
}

If I understand correctly, the following is the case:
1. I define a structure data type.
2. I then define the "var" variable within the main function to store data in the "first" structure.
3. Then I can give data to the "var" variable which is then put into the "first" structure.

[tabstop]

I now have:

#include <stdio.h>
struct first {
       int a;
       int b;
};
int main()
{
  struct first var;
  scanf(" %d", &var.a);
  scanf(" %d", &var.b);
  getchar();
  return 0;
}

If I understand correctly, the following is the case:
1. I define a structure data type.
2. I then define the "var" variable within the main function to store data in the "first" structure.
3. Then I can give data to the "var" variable which is then put into the "first" structure.

1. Sorta-kinda: you define a new data type called "struct first" (you can have a lot of different kinds of structures running around).
2. Again, sorta-kinda: you define a variable called "var" of this type "struct first" that you just did.

I'm getting the impression, just based on these three lines, that you think there's only one structure out there, which isn't true. You can have as many separate "struct first" variables as you want, and they won't interact with each other at all.

[omnificient]

Well that was very helpful. I think I understand it now!