While Loops, User Input, and Scanner

While Loops¶

(indefinite loop, we don’t know in advance how many times it will repeat!)

While Loop Syntax

while (condition) {
    statement;
    ...
}

While Loop Example

int num = 5;
while (num < 50) {
    num *= 5;
}
System.out.println(num);

While Loop Output

User Input and Scanner¶

(execute some behavior based on information the user gives us directly)

Scanner Methods¶

Method	Description
`next()`	one token as `String`
`nextLine()`	entire line as `String`
`nextInt()`	one token as `int` (if possible) throws exception if not
`nextDouble()`	one token as `double` (if possible) throws exception if not

Scanner Example

import java.util.*; // make sure you don't forget this!

public class ScannerExample {
    public static void main(String[] args) {
        //Create a Scanner object
        Scanner console = new Scanner(System.in);
        // Get next integer user input from console and stores in num
        int num = console.nextInt();
    }
}

Fenceposting¶

(pulling one iteration out of the loop)

java:Fenceposting with While Loops ExampleLh3 int num = 1; System.out.print(num); // one number to start with while (num < 5) { num++; System.out.print(", " + num); // commas between numbers }