Summary

In this lesson, you learned that:

• The if statement runs its block of code only if its condition is true. The condition goes in parentheses, the block in curly braces, and there's no semicolon after the ).
• The curly braces decide what belongs to the block. The compiler doesn't need the indentation by 4 spaces, but it shows you and others which lines belong to the block, so we always use it. We always write the braces, too, even around a single statement.
• else adds a second branch, which runs when the condition is false, and else if adds more branches with conditions of their own. The program checks the conditions from top to bottom and runs only the first true one, so their order matters.
• Comparison operators compare two values: ==, !=, >, <, >= and <=. = assigns a value, while == compares. On this site, if (points = 10) is a compile error.
• With #include <stdbool.h>, you have the type bool with the values true and false. You print them with %d as 1 and 0. In C, a condition is a number: a comparison gives 1 or 0, 0 means false, and any other number means true. A number is even when number % 2 == 0.
• Logical operators combine conditions: && (and) is true when both parts are true, || (or) when at least one is, and ! (not) turns true into false and back. Each part must be a complete comparison. Parentheses group conditions; without them, && goes before ||.
• An if statement can be nested in the block of another if. Two nested if statements without else can be rewritten as a single one with &&.
• switch chooses by the exact value of a whole number or a character: it jumps to the matching case, break ends it, and default catches everything else. Without break, the program falls through to the next case.

In the next lesson, on loops, you'll learn to make a program repeat statements: count to a hundred, for example, or add up a whole series of numbers.