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:
<while_loop> ::= "while" <condition> "{" <body> "}"Here is a simple example:
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:
<do-while> ::= "do" <statements> "while" <condition> ";"A simple example:
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:
<for_loop> ::= "for" <name> "in" <iterable> "{" <body> "}"A simple example to repeat code:
for x in 1..12 {
print("index: " + x);
}You can also use ranges to reverse the direction of the loop:
for x in 12..1 {
print("index: " + x);
}Exercices
Write a program to calculate the factorial of a given number with a while loop.
Would it be possible to solve this problem with a for loop?
Last updated