Introduction to C++

COMP282 Lectures 2022-03-07

Hello, world!

C is also valid C++ code:

#include <stdio.h>
int main() {
	printf("Hello World!\n");
}

but we can also use C++ features:

#include <iostream>
int main() {
	std::cout << "Hello World!" << std::endl;
}

Header Files

We can use C header files in C++ but there are often C++ versions of the same. For example, we can find the length of a string like so:

#include <string>
#include <iostream>
int main() {
	std::string hello = "hello";
	int x = hello.size();
	std::cout << hello << " is of length " << x;
}

In C you would use strlen().

Namespaces

Namespaces are like packages, for example:

std::cout

means that cout is defined inn the std namespace.

We can set a default namespace like so:

#include <string.h>
#include <iostream>
using namespace std;
int main() {
	string hello = "hello";
	int x = hello.length();
	cout << hello << " is of length " << x;
}

This saves us writing std:: all the time.

Input Syntax

We can use something like the following to read input:

#include <iostream>
int main() {
	std::string bla;
	int num;
	std::cin >> num >> bla;
	std::cout << bla << " " << num;
}

This can work with integers and strings, and reads up to the first space for each variable.