COMP 110 switch statements and while loops Luv Kohli September 10, 2008 MWF 2-2:50 pm Sitterson 014 1

Announcements Program 1 due Lab 2 due Friday, 2pm Chapters 1 and 2 review solutions posted on web site Program 2 assigned today 2

Questions? 3

String’s substring method 4 UNCisGreat String output = myString.substring(1, 8);

String’s substring method 5 UNCisGreat String output = myString.substring(1, 8);

Today in COMP 110 switch statements loops

Java Example: if/else Is input greater than 10? YesNo Prompt user for integer Print: “big number” Print: “small number” import java.util.*; public class FlowChart { public static void main(String[] args) { System.out.println("Give me an integer:"); Scanner keyboard = new Scanner(System.in); int inputInt = keyboard.nextInt(); if (inputInt > 10) { System.out.println("big number"); } else { System.out.println("small number"); } } }

Tracing if/else int days = 0; if (input < 6) System.out.print(“I worked ” + input + “ days this week”); else { days = input – 5; System.out.print(“I worked ” + days + “ days of overtime”); } int input = 5; int input = 6;

Example problem Write a program that takes as input your year in college (as an integer) and outputs your year as freshman, sophomore, junior, or senior

Example problem Which year? 1 Prompt user for year freshman sophomore 23 junior 4 senior Next step

With if/else if (year == 1) System.out.println(“freshman”); else if (year == 2) System.out.println(“sophomore”); else if (year == 3) System.out.println(“junior”); else if (year == 4) System.out.println(“senior”);

switch statement switch(year) { case 1: System.out.println(“freshman”); break; case 2: System.out.println(“sophomore”); break; case 3: System.out.println(“junior”); break; case 4: System.out.println(“senior”); break; default: System.out.println(“unknown”); break; } Controlling expression Case labels Break statements Default case: all other values

switch statement syntax switch (controlling expression) { case case label: statements; break; case case label: statements; break; default: statements; break; }

switch statement details Only int and char can be used in the controlling expression Case labels must be of same type as controlling expression The break statement ends the switch statement, go to the next step outside the braces in the code The default case is optional

Loops Often you need to repeat an action in a program Start Enough sandwiches? Distribute sandwiches No Yes Make sandwich

Loops Loop: part of a program that repeats Body: statements being repeated Iteration: each repetition of body Stopping condition Start Enough sandwiches? Distribute sandwiches No Yes Make sandwich

Types of loops while do-while for

while loop start; while (not enough sandwiches) { make a sandwich; } distribute sandwiches; Start Enough sandwiches? Distribute sandwiches No Yes Make sandwich

while loop syntax while (boolean expression) { statements; }

while loop The stopping condition is a boolean expression. The body code is run if the boolean expression is true. The body must be able to change the value of the boolean expression from true to false. Start Enough sandwiches? Distribute sandwiches No Yes Make sandwich

while loop Start Enough sandwiches? Distribute sandwiches No Yes Do a backflip Infinite loop!

Using a while loop Output integers from 1 to 10 int n = 1; System.out.println(n); n = n + 1; System.out.println(n); n = n + 1; System.out.println(n);... // until n == 10

Using a while loop int n = 1; while (n <= 10) { System.out.println(n); n = n + 1; }

Program 2 Due Wednesday, September 24 at 2pm NEW: In addition to ing your program, print out your program and hand it in

Friday Lab 2 due Friday, 2pm Bring laptop and textbook 25