Functions & Parameter Passing

C compilers parse code files from top to bottom. If you call a function in your `main()` method that is defined lower down in the file, the compiler will throw an error. To prevent this, place a **Function Prototype** (a declaration of the function's name, parameters, and return type) at the top of the file before `main()`, and define the function body below.

C strictly executes **Pass-by-Value** for all function calls. To modify a variable's value outside the function, you must pass its address (pointer reference) instead of its value:

• Pass-by-Value: Passing standard parameters copies the value. The original variable remains unchanged.
• Pass-by-Reference (Simulated): Passing pointer addresses allows the function to modify the original variable via dereferencing.

#include <stdio.h>

// Function prototype declarations
void changeValueVal(int x);
void changeValueRef(int *x);

int main() {
    int score = 50;

    changeValueVal(score);
    printf("After pass-by-value: %d\n", score); // Remains 50

    changeValueRef(&score);
    printf("After pass-by-reference: %d\n", score); // Updated to 100

    return 0;
}

// Function definitions
void changeValueVal(int x) {
    x = 100;
}

void changeValueRef(int *x) {
    *x = 100; // Modifies the original variable via dereferencing
}