Stage 4: Functions and Argument Passing in C++

Functions in C++: Modularity and Reusability

Functions are the basic building blocks of a program, allowing you to break down complex problems into smaller, manageable pieces. At your level, it is crucial not only to know how to write a function but also how to efficiently transfer data to it.

1. Function Structure

Every function consists of a return type, a name, a parameter list, and the function body.

cpp

return_type function_name(parameters) {
    // body
    return value; // if the type is not void
}

Important: If the function is located below the main() function, you must place its prototype (declaration) at the top of the file.

cpp

double calculateAverage(int a, int b); // Prototype

2. Passing Arguments by Value

This is the default way in C++. The function receives a copy of the variable. Changes made inside the function do not affect the original variable.

cpp

void increase(int x) {
    x = x + 10; // Only changes the local copy
}

int main() {
    int number = 5;
    increase(number);
    // number is still 5
}

3. Passing by Reference (`&`)

By using the & symbol, you create an alias for the original variable. The function operates directly on the data from the calling site. This is more efficient (no copying of large structures) and allows a function to "return" more than one value.

cpp

void actuallyIncrease(int &x) {
    x = x + 10; // Changes the original
}

4. Passing Arrays to Functions

Arrays are specific – in C++, an array passed to a function automatically "decays" into a pointer to its first element. This means the function always operates on the original, and you must additionally pass the size of the array.

cpp

void printArray(int tab[], int size) {
    for(int i = 0; i < size; i++) {
        std::cout << tab[i] << " ";
    }
}

Pitfalls and Best Practices for Exams

Returning Values (return): Remember that a function terminates immediately upon hitting a return. If a function is supposed to return an int, ensure every logical path (e.g., inside an if) ends with a return statement.
Local Variables: Variables declared inside a function cease to exist when it finishes. Never try to return a reference to a local variable!
void: Use void when a function is meant to perform an action (e.g., print text) rather than compute a value. In void functions, the return; statement (without a value) is used to exit the function early.

Example: Swap Function

This is a classic exam task testing the understanding of references:

cpp

void swap(int &a, int &b) {
    int temp = a;
    a = b;
    b = temp;
}

Functions in C++: Modularity and Reusability

1. Function Structure

Every function consists of a return type, a name, a parameter list, and the function body.

cpp

return_type function_name(parameters) {
    // body
    return value; // if the type is not void
}

Important: If the function is located below the main() function, you must place its prototype (declaration) at the top of the file.

cpp

double calculateAverage(int a, int b); // Prototype

2. Passing Arguments by Value

This is the default way in C++. The function receives a copy of the variable. Changes made inside the function do not affect the original variable.

cpp

void increase(int x) {
    x = x + 10; // Only changes the local copy
}

int main() {
    int number = 5;
    increase(number);
    // number is still 5
}

3. Passing by Reference (`&`)

cpp

void actuallyIncrease(int &x) {
    x = x + 10; // Changes the original
}

4. Passing Arrays to Functions

cpp

void printArray(int tab[], int size) {
    for(int i = 0; i < size; i++) {
        std::cout << tab[i] << " ";
    }
}

Pitfalls and Best Practices for Exams

Returning Values (return): Remember that a function terminates immediately upon hitting a return. If a function is supposed to return an int, ensure every logical path (e.g., inside an if) ends with a return statement.
Local Variables: Variables declared inside a function cease to exist when it finishes. Never try to return a reference to a local variable!
void: Use void when a function is meant to perform an action (e.g., print text) rather than compute a value. In void functions, the return; statement (without a value) is used to exit the function early.

Example: Swap Function

This is a classic exam task testing the understanding of references:

cpp

void swap(int &a, int &b) {
    int temp = a;
    a = b;
    b = temp;
}

Stage 4: Functions and Argument Passing in C++

Functions in C++: Modularity and Reusability

1. Function Structure

2. Passing Arguments by Value

3. Passing by Reference (`&`)

4. Passing Arrays to Functions

Pitfalls and Best Practices for Exams

Example: Swap Function

You might also like

Stage 11: Pointer Arithmetic in C++

Stage 10: Pointers, Address-of, and Dereference Operators

Stage 6: C-Style String Handling (char[])

Stage 4: Functions and Argument Passing in C++

Functions in C++: Modularity and Reusability

1. Function Structure

2. Passing Arguments by Value

3. Passing by Reference (`&`)

4. Passing Arrays to Functions

Pitfalls and Best Practices for Exams

Example: Swap Function

You might also like

Stage 11: Pointer Arithmetic in C++

Stage 10: Pointers, Address-of, and Dereference Operators

Stage 6: C-Style String Handling (char[])

Functions in C++: Modularity and Reusability

1. Function Structure

2. Passing Arguments by Value

3. Passing by Reference (&)

4. Passing Arrays to Functions

Pitfalls and Best Practices for Exams

Example: Swap Function

You might also like

Stage 11: Pointer Arithmetic in C++

Stage 10: Pointers, Address-of, and Dereference Operators

Stage 6: C-Style String Handling (char[])

Functions in C++: Modularity and Reusability

1. Function Structure

2. Passing Arguments by Value

3. Passing by Reference (&)

4. Passing Arrays to Functions

Pitfalls and Best Practices for Exams

Example: Swap Function

You might also like

Stage 11: Pointer Arithmetic in C++

Stage 10: Pointers, Address-of, and Dereference Operators

Stage 6: C-Style String Handling (char[])

3. Passing by Reference (`&`)

3. Passing by Reference (`&`)