# Loops Now I will introduce you the concept of loops. A loop can repeat code. There are several kind of loops but we will start with the simplest loop - The `while` loop. ## While Loops The while loop is a head-controlled loop. That means that the body will only be executed if the condition is true, otherwise the body will be skipped. Here is the syntactic structure: ```ebnf ::= "while" "{" "}" ``` Here is a simple example: ```sc func main() { let mut number = 42; while number > 0 { //only execute if number is greater than zero print(number); //prints the number number = number + 1; //increses number by 1 } } ``` ## Do-While Loops The do-while loop is a foot-controlled loop. The body will always be executed and stops if the condition is false. The struture: ```ebnf ::= "do" "while" ";" ``` A simple example: ```sc func main() { let mut input : string = none; do { input = Console::ReadLine(); print("echoed $input"); } while input != "exit"; } ``` This sample expects an userinput and write it back only if the user types not `exit`. ## For-Loop A for loop can be used to iterate over arrays/iterators. To repeat code for a given number of iterations you can use ranges. The definition of a for-loop: ```ebnf ::= "for" "in" "{" "}" ``` A simple example to repeat code: ```sc for x in 1..12 { print("index: " + x); } ``` You can also use ranges to reverse the direction of the loop: ```sc for x in 12..1 { print("index: " + x); } ``` ## Exercices 1. Write a program to calculate the factorial of a given number with a while loop. 2. Would it be possible to solve this problem with a for loop?