How do I use a structure?

Question

Ok firstly I\'ll explain my assignment. For this assignment I have to use dynamic memory allocation which I am having no problems with. What I am having a problem with is fi

Answer 1

You're redefining studentData

int * studentData= NULL;

then later

studentDataType *studentData = (studentDataType*)malloc(numberOfStudents * sizeof(studentData));

You should declare the studentDataType struct first (outside of main() ) then use it in your original declaration

Answer 2

The first problem is that you have variable names the same as the name of the type. Although you can have that in C to a certain extent, like:

typedef int x;
x foo (x x)
{
  return x;
}

It might be a good idea not to do this for the readability purposes. So in your case you have:

int * studentData= NULL;
int * studentDataType= NULL;

which is a variable name, then you have:

struct studentDataType ...

which is a name of the type (should be used as struct studentDataType, not without struct as you do); finally

studentDataType *studentData = ...

is treated by the compiler as an operation on two variables, not a type declaration as you would expect. So your memory allocation needs to be:

struct studentDataType *studentData = malloc(numberOfStudents *sizeof(struct studentData));

Which brings a problem that you redefine studentData, which you declared in the beginning of the program, and "numberOfStudents" is not defined, probably you wanted to write "students" instead.

As for the reading data with scanf, see the previous comment.

Answer 3

To see the task it is better at least for the first time to write some block-scheme of what you have to do in a program. In your case:

1. Read data from user (each structure).
2. Increase array size, add new structure.
3. Loop 1-2 until input user finish adding new people (needs some condition here to finish).
4. Find necessary structure and print it.

So the first step is to read information from user. You can use scanf(): In the simplest way you can do that step-by-step for each field:

#include <stdio.h>
...
int value;
scanf("%d", &value);
...

In case of success this function should return number of items it reads (1 in your case). For phone you should use scanf("%ld", &phone).

To resize array use function realloc() (#include :

realloc(&ptr_to_array, new_size);

Each elements of the array is a pointer to structure "student". Next steps are similar.