Getting multiple struct entries from stdin - c

Question

I am trying to get multiple entries for my struct via the keyboard. I think I am wrong inside of scanf but I am not sure where I am wrong. Thanks!
Here is what I have:
#include <stdio.h>
#include <math.h>
int main()
{
//define the structure
struct course
{
char title[20];
int num;
} ;
// end structure define
//define the variable
struct course classes;
printf("Enter a course title and course number");
scanf("%s %d", classes[3].title, &classes.num);
return 0;
}

Answer 1

Fix the code as Carl said and it works fine:
#include <stdio.h>
int main()
{
struct course
{
char title[20];
int num;
} ;
struct course class;
printf("Enter a course title and course number");
scanf("%s %d", class.title, &class.num);
printf("%s %d", class.title, class.num);
return 0;
}

Answer 2

There are a couple issues.
You have this struct called "classes", but it has only 1 entry - you're accessing the 3rd entry so you're running off the end.
Also, Title is 20 bytes long, but if you enter something larger in scanf(), it will just overflow. The basic scanf() structure looks ok though.
I would set it up more like this:
#include <stdio.h>
#include <math.h>
#define MAX_CLASSES 50 // how big our array of class structures is
int main()
{
//define the structure
struct course
{
char title[20];
int num;
} ;
// end structure define
//define the variable
struct course classes[MAX_CLASSES];
int nCurClass = 0; // index of the class we're entering
bool bEnterMore = true;
while (bEnterMore == true)
{
printf("Enter a course title and course number");
scanf("%s %d", classes[nCurClass].title, &classes[nCurClass].num);
// if user enters -1 or we fill up the table, quit
if (classes[nCurClass].num == -1 || nCurClass > MAX_CLASSES-1)
bEnterMore = false;
}
}
That's the basic idea. Another improvement that could be made would be checking the length of the course title before assigning it to classes[].title. But you need something to do ;-)