5. Function

Today’s Outline

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• Defining a Function
• Calling a Function
• Declare a Function
• Passing Parameters
• Recursive Functions

Defining a Function

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void printHello (int n) {
    for (int i = 0; i < n; i++) {
        cout << "Hello" << endl;
    }
}

Calling a Function

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void main() {
    int x = 4;
    printHello(x);
}

Function in C++ Library

• #include <cmath> - Mathematical Calculations
• #include <cstring> - String Manipulations
• #include <iostream> - Input/Output

Function in Memory Stack

Declare a Function

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Function Prototype

int findMax(int, int); // Function Prototype
 
void main() {
    cout << findMax(3, 4);
}
 
int findMax(int x, int y) {
    return x > y ? x : y;
}

• The function must be declared before use
• The function prototype is the declaration of the function
• The implementation of the function can be defined later

Header file (.h)

• Contains function prototype only
• To be included in the program that will call the function

Implementation file (.cpp)

• Contains function implementation

Passing Parameters

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Argument vs Parameter

Parameter Passing in C++

• Pass-by-Value
• Pass-by-Reference
• Pass-by-Pointer (Later)

Pass-by-Value

Pass-by-Reference

Parameter Passing: Default Parameters

void f(int a, int b = 0) {
    cout << a << " " << b << endl;
}

• Default parameters must be defined from the last parameter

Recursive Functions

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Iterative vs Recursive

Efficiency of Recursion

• Generally speaking, non-recursive versions will execute more efficiently (time/space)

Summary

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• Define, call, and declare functions
• Parameter passing
  • By Value
  • By Reference
• Recursive functions