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CSC111
Quick Revision

Problem
We want to develop a Java program to calculate the average of
numbers entered by the user. The average is calculated as follows
Average= sum \ count of numbers
Your program should ask the user to enter numbers and stops if:
1) The user enters -999.
2) Or the user enters 10 numbers.
Analysis
 Input
 Number

processing



Take numbers from user
Calculate the sum
Calculate the average
 Output
 Average
Design
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Start the program
Read number from user and save it in number.
Declare variable count and initialize it to zero.
Declare variable sum and initialize it to zero.
While number is not equal to -999 and count is less than 30 numbers
Calculate sum using -> (sum + number)
Increment count by 1.
Now repeat
Calculate Average using -> (sum \ count).
print the average.
End the Program
Coding

Start the program

1. Start by writing the
program structure
/* We want to develop a Java program to calculate the
average of numbers entered by the user */
//Aseel Alkhelaiwi
// import Section – import used java libraries
public class Average{
// main method
public static void main( String args[] ){
// Declaration section – Declare needed variables
// Input section – Enter required data
// Processing section – Processing Statements
// Output section – Display expected results
} // end main
} // end class
Variable Declaration

What variable do I need ??
 input

number
 Processing


sum
count
Variable Declaration
 what about data type
 input

number
int
 Processing


sum
count
int
int
2. Declare variable
Note:
• if some variable has initial value
// import Section – import usedinitialize
javathem
libraries
public class Average{
• Use appropriate variable name
// main method
public static void main( String args[] ){
// Declaration section – Declare needed
variables
int number;
int sum=0 ;
int count =0;
// Input section – Enter required data
// Processing section – Processing
Statements
// Output section – Display expected
results
} // end main
} // end class
3.Input
Reading input from the user
• 4 basic steps
 Step 1: import the Scanner class:
 import java.util.Scanner;
 Step 2 : declaring a reference variable of a Scanner
 Scanner input ;
 Step 3: creating an instance of the Scanner
 input = new Scanner (System.in);
 Step 4: use specific methods to enter data
 int number = input.nextInt();
/// import Section – import
used java libraries
import java.util.Scanner;
public class Average{
// main method
public static void main(
String args[] ){
// Declaration section –
Declare needed variables
// to store numbers
int number;
// to store the sum
int sum=0 ;
//to store the count of
numbers
int count =0;
input=new Scanner (System.in);
//read number
System.out.println("Enter
number");
number=input.nextInt();
} //end main
} //end class
Scanner input;
• Print message before each
read
4.Processing
There are two conditions that need to be met to enter the while
loop:
1)the number entered not equal to -999
Written as : while (number != -999)
2) the numbers entered are less than or equal to 10.
HOW!!
by counting the numbers entered by the user. Once the amount
exceeded 10
we will exit the loop
Written as : while ( count <10)
4.Processing
When 1 and 2 combined the while loop is written as:
while ( number != -999 && count < 10)

//import Section – import used java
libraries
import java.util.Scanner;
public class Average{
// main method
public static void main( String
args[] ){
// Declaration section – Declare
needed variables
int number; // to store numbers
int sum=0 ; // to store the sum
int count =0; // to store the count
of numbers
Scanner input;
input=new Scanner (System.in);
//read number
System.out.println("Enter number");
number=input.nextInt();
while (number != -999 && count < 10){
sum = sum +number;
count ++;
System.out.println("Enter another number");
number=input.nextInt();
} // end while
// Output section – Display expected results
if (count != 0)
System.out.printf("The average =
%d%n",(sum / counter));
else
System.out.println("No input.");
} // end main
// Processing section – Processing
Statements
} // end class
Sample Run
Enter number
10
Enter another number
15
Enter another number
5
Enter another number
-999
The average = 10
Same Question in Flag-controlled While Loop
boolean done = false;
while (number != -999 && count < 10){
while ( !done){
sum = sum +number;
system.out.println("Enter number");
count ++;
number=input.nextInt();
System.out.println("Enter another number");
if (number == -999 || count >=10)
number=input.nextInt();
} // end while
done = true;
else {
sum = sum + number;
count++;
} // end else
} // end while
Same Question but Flag-controlled While Loop

//import Section – import used
java libraries
import java.util.Scanner;
public class Average{
// main method
public static void main(
String args[] ){
// Declaration section –
Declare needed variables
int number; // to store
numbers
int sum=0 ; // to store the
sum
int count =0; // to store the
count of numbers
boolean done= false;
Added
Scanner input;
input=new Scanner (System.in);
//read number
// Processing section – Processing
Statements
while ( !done){
system.out.println("Enter number");
number=input.nextInt();
if (number == -999 || count >=10)
done = true;
else {
sum = sum + number;
count++;
} // end else
}// end while
// Output section – Display expected
results
if (count != 0)
System.out.printf("The average =
%d%n",(sum / counter));
else
System.out.println("No input.");
} // end main
} // end class
In the question above we saw that:
The same question could be written in
different forms of while loops.