Functions, Passing by Address

void swap(int x, int y){
	int temp = x;
	x = y;
	y = temp;
}

int main(){
	int x = 10, y = 5;
	cout << "Before: x = " << x <<", y = " << y << endl;
	swap(x,y);
	cout << "After: x = " << x <<", y = " << y << endl;
}

void swap(int*x, int*y){
	int temp = *x;
	*x = *y;
	*y = temp;
}

int main(){
	int x = 10, y = 5;
	cout << "Before: x = " << x <<", y = " << y << endl;
	swap(&x,&y);
	cout << "After: x = " << x <<", y = " << y << endl;
}

Pass by Reference

• Something new in C++ that lets functions see and operate memory without using address
• Syntax for defining a reference: int&x or int& x or int &x.
• A C++ reference uses less memory than a C pointer since you don’t have to store the address being pointed to

void swap(int&x, int&y){
	int temp = x;
	x = y;
	y = temp;
}

int main(){
	int x = 10, y = 5;
	cout << "Before: x = " << x <<", y = " << y << endl;
	swap(x,y);
	cout << "After: x = " << x <<", y = " << y << endl;
}

int a = 7, b = 12;
int& ra = a;   // ra now refers to a, whose value is 7
ra = b   // this doesn't do any reassigning, you just made ra = a = b = 12

• You cannot reassign a reference. You must initialize them at declaration. Reassigning a reference will change the value at that location in memory.

int x = 10;
int &y = x;
y = 20;

1. x = 20, y = 20
2. x = 20, y = 10
3. x = 10, y = 20

Compiling Single Files

#include <iostream>
using namespace std;

void printNum(int x){
	cout << "The value is " << x << endl;
}

int userInputNum(){
	int x;
	cout << "Enter an integer " << endl;
	cin >> x;
	return x;
}

int main(){
	int num = userInputNum();
	printNum(num);
	cin >> num;
}

• To compile this file using g++, use the compiler + source code name + output .exe name as such: g++ main.cpp -o main
• To run this file, you type ./main
• g++ -c main.cpp → this is the compiler giving us main.o, a binary object file
• g++ main.o -o main → this is the linker linking the object file to an executable