Conditions: if / else / switch

Teach your program to make decisions

Big Idea: A program does not have to run the same way every time. With conditions it can look at a value and choose what to do next: run this block, or that one. This is how a program becomes smart.

By the end you will be able to:

use if to run code only when something is true,
use if / else to pick between two paths,
chain else if to test several conditions in order,
use switch to choose cleanly among many fixed values.

1. The idea: a fork in the road

Imagine walking and reaching a fork in the road. You ask a yes/no question — "Is it raining?" — and pick a path based on the answer. Your program does the same. It checks a condition (a question that is either true or false) and runs different code for each answer.

In C++ we ask these questions with comparison operators. Each one gives back true or false:

Operator	Means	Example (true when)
`==`	is equal to	`x == 5` (x is 5)
`!=`	is not equal to	`x != 5` (x is not 5)
`>`	greater than	`x > 5`
`<`	less than	`x < 5`
`>=`	greater than or equal	`x >= 5`
`<=`	less than or equal	`x <= 5`

Careful: == asks "are these equal?" while a single = assigns a value. They are not the same!

2. The `if` statement

An if runs a block of code only when its condition is true. If the condition is false, the block is skipped.

#include <iostream>
using namespace std;

int main() {
    int age = 20;

    if (age >= 18) {
        cout << "You are an adult." << endl;
    }

    return 0;
}

Output: You are an adult.

Because age is 20 and 20 >= 18 is true, the message prints. If age were 12, the condition would be false and nothing would print. The { } braces hold everything the if controls.

Conditions: if / else / switch