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Counting Loops
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
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: 12345
– Code that now.
Repetition Code
int intNumber = 1;System.out.println(intNumber);intNumber = intNumber + 1;System.out.println(intNumber);intNumber = intNumber + 1;System.out.println(intNumber);intNumber = intNumber + 1;System.out.println(intNumber);intNumber = intNumber + 1;System.out.println(intNumber);
Repeat More Often
• Change count to 10 times. • Annoying???• See the repetition?• Loop the same commands over and over
again in a pattern
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
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);
Flowchart of For…Next Loop
Chapter 5 – Slide 8
intCount <= 10? Display "Hello"
Yes
No
Set intCount to 1
Add 1 to intCount
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 ___
Your Code with a Loop
int intNumber ; for (intNumber = 5;
intNumber <= 50;intNumber= intNumber+5) {
System.out.println(“Inside loop “+ intNumber);
} System.out.println(“After loop: “ + intNumber);
starttest increase
Add Up
• Need a bucket to hold the total• Start at 0• Keep accumulating each pass• Make your numbers sum up
Logic for Keeping a Running Total
Chapter 5 – Slide 12
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
Code that Totals
int intSum = 0; int intNumber ; for (intNumber = 1;
intNumber <= 5;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);
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 haveSystem.out.println(total);
at end of first loop, count = 1 and total = 1 +0 = 1at end of second loop, count = 2 and total = 2 + 1 = 3at end of third loop, count = 3 and total = 3 + 3 = 6at end of entire loop, count is gone and total = 3
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.
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);
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!