Menu Driven programs in Java

Menu Driven programs in Java, infinte loop, do while loop, calculator program in java

1. Intro to Java
Session 17,18
Menu-driven programs

2. Contents
•Multi-way selection
•Infinite loop
•Loop with post-condition
•Menu program

3. The ‘switch’ statement
Aswitchstatementmaybeusedwhen
 onlyonevariableisbeingcheckedineachcondition
 thecheckinvolvesspecificvaluesofthatvariable
(e.g.'A','B')andnotranges(e.g.>39);

4. The ‘switch’statement: an example
chargroup;
System.out.println("Enteryourgroup(A,B,C)");
group=EasyIn.getChar();
switch(group)
{
case'A':System.out.print("10.00a.m");
break;
case'B':System.out.print("1.00p.m");
break;
case'C':System.out.print("11.00a.m");
break;
default:System.out.print("Nosuchgroup");
}

5. Infinite loop
•An infinte loop is a loop that will execute indefinitely because
the loop's expression is always true
Syntax:
while(true)
{
….
statements to be repeated;
break;
}
•Make sure you there is break; statement of System.exit(0);
inside the body of the loop.
•These statements will let you come out of the loop. Otherwise,
the loop will execute indefinitely.

6. import java.util.Scanner;
public class Menu
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
System.out.println("::Welcome to Menu driven code::");
while(true)
{
System.out.println("To execute case 1, Enter value 1");
System.out.println("To execute case 2, Enter value 2");
System.out.println("To Exit, Enter value 9");
System.out.println("Enter your choice::");
int choice = scan.nextInt();
switch(choice)
{
case 1: System.out.println("I am case 1");
break;
case 2: System.out.println("I am case 2");
break;
case 9: System.out.println("Exiting the application");
System.exit(0);
default: System.out.println("Incorrect input!!! Please re-enter");
}
}
}
}
Template for writing any
menu driven program using infinite loops:

7. import java.util.Scanner;
public class Main {
public static void main(String[] args)
{
Scanner reader = new Scanner(System.in);
while(true)
{
System.out.print("Enter two numbers: ");
double first = reader.nextDouble();
double second = reader.nextDouble();
System.out.print(“Enter (+, -, *, /): or # to exit ");
char operator = reader.next().charAt(0);
double result;
switch (operator)
{
case '+':
result = first + second;
break;
case '-':
result = first -second;
break;
case '*':
result = first * second;
break;
case '/':
result = first / second;
break;
case '#':
System.exit(0);
// operator doesn't match any case constant (+, -, *,
/)
default:
System.out.printf("operator is not correct");
return;
}
System.out.println(first + " " + operator + " " +
second + " = " + result);
}
}
}
Calculator Program

8. The‘do…while’loop
Thedo…whileloophasitswhileconditionatthe
endoftheloopratherthanatthebeginning.
If the while condition is at the end of the loop, the loop
will iterate at least once.
do
{
//instruction(s)toberepeatedgohere
}while(/*testgoeshere*/);

9. The ‘do...while’ loop: an example
charresponse;
do
{
//programinstructionsgohere
System.out.println("another go(y/n)?");
response=EasyIn.getChar();
}while(response=='y');

10. charresponse;
System.out.println("***Lab Times***");
do
{
System.out.println();
System.out.println("[1]TIMEFORGROUPA");
System.out.println("[2]TIMEFORGROUPB");
System.out.println("[3]TIMEFORGROUPC");
System.out.println("[4]QUITPROGRAM");
System.out.print("enterchoice[1,2,3,4]:");
response=EasyIn.getChar();
System.out.println();
switch(response)
{
case'1':System.out.println("10.00a.m");break;
case'2':System.out.println("1.00p.m");break;
case'3':System.out.println("11.00a.m");break;
case'4':System.out.println("Goodbye ");break;
default:System.out.println("Options 1-4only!");
}
}while(response!='4');
An example of a menu driven program using do while loop

11. Interacting
with a menu
driven
program
[1]TIMEFORGROUPA
[2]TIMEFORGROUPB
[3]TIMEFORGROUPC
[4]QUITPROGRAM
enterchoice[1,2,3,4]:5
Options1-4only!
[1]TIMEFORGROUPA
[2]TIMEFORGROUPB
[3]TIMEFORGROUPC
[4]QUITPROGRAM
enterchoice[1,2,3,4]:1
10.00a.m
[1]TIMEFORGROUPA
[2]TIMEFORGROUPB
[3]TIMEFORGROUPC
[4]QUITPROGRAM
enterchoice[1,2,3,4]:4
Goodbye