Conditionals

You make hundreds of decisions every day: if it rains, you take an umbrella, otherwise you don't. When the alarm rings, you get up. Programs work the same way: they check a condition and then decide what happens next. That is exactly what you will explore now.

If, then, else

A conditional, also called an if statement, is a fork in the road of your program. It has three parts: the condition itself (if), a branch for when the condition is true (then), and a branch for when it is false (else). The program always follows only one of the two paths, never both at once.

Conditions are comparisons

A condition is almost always a comparison between two values: is one number greater than another? Smaller? Or exactly equal? Every comparison has exactly one answer: true or false. The comparison 7 greater than 5 is true, the comparison 3 equals 4 is false. Watch out for the borderline case: greater than means strictly greater, less than means strictly less. That is why 9 less than 9 is false, because 9 is exactly as big as 9. With that answer, the program knows which branch to take.

Checking several cases in a row

Often there are more than two possibilities. Then the program checks several conditions one after another: if the first one is true, its branch runs and the rest is skipped. If not, the next condition gets its turn, and so on. The order matters: the first condition that is true always wins.