How Data is Transferred

When you pass a variable to a function, C needs to decide how to handle that memory. There are two primary techniques, each with its own specific use cases.

1. Call by Value (The Safe Default)

A copy of the variable's value is created and handed to the function.

• The function works on this "clone."
• Changes made inside the function do not affect the original variable in the caller.
• Analogy: You give someone a photocopy of your document. They can scribble on it, but your original document stays clean.

void changeValue(int n) {
    n = 100; // Only changes the clone
}

2. Call by Reference (Using Pointers)

Instead of a copy, the memory address of the variable is passed to the function.

• The function uses a pointer to "look at" the original memory spot.
• Changes made inside the function will affect the original variable.
• Analogy: You give someone the key to your house. Whatever they change inside the house will be there when you get home.

void changeValue(int *n) {
    *n = 100; // Changes the actual variable in main!
}

Which one should I use?

Returning Multiple Values

In C, a function can only return one value using the return statement. If you need to "return" three things, you must pass three variables by reference and have the function update them.

Strictly speaking, C is always "Call by Value." In "Call by Reference," you are simply passing the value of the memory address! It's a subtle but important distinction in computer science.