WARM-UP: MON, APR 7• What are loops used for in

programming?

• What are at least 2 different kinds of loops?

CHAPTER 5: LOOPSPRE-AP COMPUTER SCIENCECYCLE 6

REVIEW: IF STATEMENTS• Used to make decisions/answer

questions

• Formed using a conditional statement• Conditional operators

• IF IF-ELSE IF – ELSE-IF – ELSE

IF STRUCTUREif (condition1) { //statements}else if (condition2) { //statements}else { //statements}

LOOPS• Used to repeat tasks

• Benefits• Reduce amount of code required• Reduce copy-pasting / repetition• Increase code efficiency (speed)• Makes code more readable / easier to

understand

TYPES OF LOOPS• WHILE Loops

• Tasks with unknown stopping points• “infinite” loops

• DO-WHILE Loops• Tasks with unknown stopping points that

MUST execute at least once

• FOR Loops• Repeat ‘x’ times

TYPES OF LOOPS• WHILE Loops

• Tasks with unknown stopping points• “infinite” loops

• DO-WHILE Loops• Tasks with unknown stopping points that

MUST execute at least once

• FOR Loops• Repeat ‘x’ times

WHILE LOOPS - STRUCTUREwhile (condition) { //statements //counter/environment change}

WHILE LOOPS - STRUCTUREwhile (condition) { //statements //counter/environment change}

Statements – the tasks you want repeatedCounter change – prevents infinite loops

EXAMPLE A: PRINT 1 THRU 100 int number = 1;while (number <= 100){

System.out.println(number);number++;

}

EXAMPLE B: PRINT 1 THRU AN INPUTTED NUMBERint number = 1;int stop = console.nextInt();while (number <= stop){

System.out.println(number);number++;

}

EXAMPLE C: PRINT 10 MULTIPLES OF AN INPUTTED NUMBERint multiple = 1;int number = console.nextInt();while (multiple <= 10){

System.out.println(number*multiple);multiple++;

}

WARM-UP: APR 8Write the standard structure for a WHILE loop.

Why is it necessary to change the counter or environment inside of a WHILE loop? What will happen if you do not?

WARM-UP: APR 9Correct the following code so that it finds the sum of 10 numbers.

int sum = 0;while (count < 10)

num = console.nextInt();sum = sum + num;count++;

REVIEW: WHILE LOOPS• Typically used for looping situations where

you do not know how many times the loop will iterate

• Not always counter-controlled

while (condition) {//statements//counter/environment change

}

EXAMPLE: PRINT 1 THRU AN INPUTTED NUMBERint number = 1;int stop = console.nextInt();while (number <= stop){

System.out.println(number);number++;

}

FOR LOOPS• Typically used in looping situations

where the number of iterations is known

• Always counter controlled

FOR LOOPS - STRUCTUREfor (start; stop; change){

//statements}

Start, stop, change refer to the counter

EXAMPLE A: PRINT THE NUMBERS 1 THRU 100

int counter;for (counter=1; counter<=100; counter++){

System.out.println(counter);}

EXAMPLE B: PRINT THE WORD “HELLO” 5 TIMES

int i;for (i=1; i<=5; i++){

System.out.println(“Hello”);}

EXAMPLE C: PRINT OUT ALL EVEN NUMBERS BETWEEN 0 AND 1000

for (int num=0; num<=1000; num=num+2){

System.out.println(num);}

FOR VS WHILEWHILE

int i=0;while (i < 100){ System.out.print(i); i++;}

FORfor (int i=0; i < 100; i++){ System.out.print(i);}

WARM-UP: APR 10 • Write a FOR loop that would loop 25

times with a counter that begins at 12.

QUIZ TOMORROW!