1. Counting Loops

2. Introduction to Loops: The Counting Loop
Chap 2 section 2.3
A loop is a repeating structure that contains a block of program statements.
Needs a way to indicate which statements repeat
Needs a way to start

3. Repeat Something
The a parameter sets a number on and the program needs to count up to that number by displaying each number on the console until it reaches that number
Assume the parm is going to hold 5. The program should show: 1 2 3 4 5
Code that now.

4. Repetition Code
int intNumber = 1; System.out.println(intNumber); intNumber = intNumber + 1;

5. Repeat More Often Change count to 10 times. Annoying???
See the repetition?
Loop the same commands over and over again in a pattern

6. Loop Syntax Tell the computer to loop To do it 5 times:
Setup: Create an integer to count with
Start where? Start at 1
Increment? Keep adding 1 your integer
Stop where? Stop at 5
Watch your counter by printing it
During
After

7. Your Code with a Loop
int intNumber ; for (intNumber = 1; intNumber <= 5; intNumber= intNumber+1) { System.out.println(“Inside loop “ + intNumber); } System.out.println(“After loop: “ + intNumber);

8. Flowchart of For…Next Loop
intCount
<= 10?
Display "Hello"
Yes No
Set intCount to 1
Add 1 to intCount

9. You try it - Counting Count from 5 to 50 by 5’s
Setup: Create an integer to count with
Start where? Start at ___
Increment? Keep adding ___ your integer
Stop where? Stop at ___

10. Your Code with a Loop start test increase
int intNumber ; for (intNumber = 5; intNumber <= 50; intNumber= intNumber+5) { System.out.println(“Inside loop “ + intNumber); } System.out.println(“After loop: “ + intNumber);

11. Add Up Need a bucket to hold the total Start at 0
Keep accumulating each pass
Make your numbers sum up

12. Logic for Keeping a Running Total
Read the next number
Is there another number to read?
Set accumulator to 0
Add the number to the accumulator
Yes
(True) No
(False)
Setting the accumulator variable to zero
before entering the loop is a critical step

13. Code that Totals int intSum = 0; int intNumber ; for (intNumber = 1;
intNumber= intNumber+1) {
intSum = intSum + intNumber;
System.out.println(“Inside loop “ + intNumber ); System.out.println(“running count: “ + intSum ); }
System.out.println(“After loop total: “ + intSum);

14. Accumulating a total Variables don't remember what they were
You can create a variable to increase and run it each time the loop runs.
double total = 0;
for (int count = 1; count <= 3; count++)
{ total = total + count;} // add what you are counting to what you have
System.out.println(total);
at end of first loop, count = 1 and total = 1 +0 = 1
at end of second loop, count = 2 and total = = 3
at end of third loop, count = 3 and total = = 6
at end of entire loop, count is gone and total = 3

15. You try – totalling
What is the total of the series from 5 to 50 by 5’s?
Create a variable to hold the total
Set that variable to 0 – before you start repeating
Add to the variable repeatedly (inside loop)
After the loop – you have your total.

16. Your Code Totalling with a Loop
int intNumber ; int intSum= 0; for (intNumber = 5; intNumber <= 50; intNumber= intNumber+5) { intSum = intSum + intNumber; System.out.println(“Inside loop “ + intNumber ); System.out.println(“running count: “ + intSum ); } System.out.println(“After loop total: “ + intSum);

17. Summary of Loops Repetition Starts with For () {
Ends with : matching }
Starting value: 1rst statement inside ()
Go Condition – 2nd statement inside ()
Increment – last statement inside ()
Total –
Create bucket starting at zero
Accumulate inside loop
Have total after loop
Next: Loops inside loops!