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// This file provides a "first program" in C++.
#include <iostream>
// ^-- this is a "preprocessor directive", which tells the compiler to include
// the contents of the system header iostream. It contains declarations
// of the standard input/output streams (std::cin, std::cout & std::cerr),
// which are used to read and write data from the terminal.
#include <string>
// ^-- this is another system header, which contains declarations of the
// string type, which is used to represent strings of characters.
// This is an example of a function definition, this function takes an integer
// as input and returns a boolean (true or false) as output.
bool isPrime(int n) {
if (n < 2) {
return false;
}
// Try dividing by all numbers from 2 to sqrt(n).
for (int i = 2; i*i < n; ++i) {
if (n % i == 0) {
return false;
}
}
// If we get here, we didn't find a factor, so n is prime.
return true;
}
int main() {
std::cout << "What is your name? (one word only please) ";
// ^-- to print things out, we use std::cout (the output stream
// representing the default output device, which is usually the
// terminal) with the << operator, which is known as the "stream
// insertion operator". The << operator is overloaded for many
// different types, so we can use it to print out strings, ints,
// doubles, etc.
std::string name;
// ^-- this declares a variable named "name" of type std::string.
std::cin >> name;
// ^-- to read things in, we use std::cin (the input stream representing
// the default input device, which is usually the terminal) with the
// >> operator, which is known as the "stream extraction operator".
// The >> operator is overloaded for many different types, so we can
// use it to read in strings, ints, doubles, etc.
// Note that the line above reads a single word, if we wanted to read
// the whole line, we could instead use:
// std::getline(std::cin, name);
std::cout << "Hello, " << name << "!" << std::endl;
// ^-- the << operator can be used multiple times in a single statement,
// so we can print out multiple things in a single line. This works
// because the << operator returns the same stream that it was called
// on, so we can chain multiple << operators together.
// std::endl is a special value that represents the end of a line.
std::cout << "What is your favorite number? ";
int number;
std::cin >> number;
std::cout << "Your favorite number is " << number;
// ^-- we've applied the same ideas to reading in an integer and printing
// it out, notice that we didn't need to use std::endl here because
// we're going to print out more stuff on the same line.
if (isPrime(number)) {
std::cout << ", and that's a prime number!" << std::endl;
} else {
std::cout << ". It's not a prime number, but that's okay!" << std::endl;
}
return 0;
// ^-- main must return an integer, and 0 is the standard value to return
// if the program exits successfully. Any other value indicates that
// the program exited with an error.
}
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