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Let’s wrap up by using structures with functions.

We can specify structures and pointers to structures as parameters to functions:

void myFunction(struct Bottle b, struct Bottle* bPointer)

When passing a structure to a function:

  • A copy of the structure is made so memory usage is a concern
  • Any modifications made to the structure will not affect the original structure, only the copy

When passing a pointer to a structure:

  • Because the pointer is the address of the original structure any modifications to the member variables will affect the original structure
void bottleFunction(struct Bottle b, struct Bottle* bPointer){ b.name = "Super Large"; b.maxCapacity = 100; bPointer->name = "Super Small"; bPointer->maxCapacity = 4; } int main(){ struct Bottle b1 = {“Medium”, 24, 9}; struct Bottle b2 = {“Large”, 35, 9}; bottleFunction(b1, &b2);

In the above example:

  • bottleFunction has 2 parameters, a Bottle structure and a pointer to a Bottle structure
  • Inside the function, the structures are accessed the same as they would whether it is a structure or pointer to a structure.
  • The first argument in the call to bottleFunction() inside main() is b1. A copy of this structure is made within bottleFunction() and no changes can be made to the values of b1 in main()
  • The second argument in the call to bottleFunction() is &b2: the address of b2. Any change to the member variables using this address will change the values of b2 in main()

We can also return structures by setting the return type in the function signature:

struct Bottle getEmptyBottle(void){ struct Bottle b = {"My Bottle", 24, 0}; return b; }

Notice that structures as parameters and as the return type must use the struct keyword.

Instructions

1.

Time to look at different ways we can work with structures within functions.

In script.c:

  • Define the function ageOne()
  • Give the function a return type of Person
  • The body can be empty.

Remember to use the keyword struct throughout this definition.

2.

Add some parameters to the ageOne() function definition:

  • The first function parameter should be called friend1 and be of type Person
  • The second parameter should be called friend2Pointer and be a pointer to type Person
3.

Now modify the age member variables within the structures.

Inside ageOne():

  • Add 1 to the age variable in friend1
  • Using the arrow format to dereference, add 1 to the age variable in the structure pointed to by friend2Pointer
  • Return the structure friend1
4.

Now test it all out! There are 2 structures defined in main() to work with the function you created.

Inside the main() function:

  • Call ageOne() and assign the return value to myFriend
  • Set the first argument of ageOne() to myFriend
  • Set the 2nd argument of ageOne() to the address of myOtherFriend

Run the code and see how the data changes.

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