warm-up: mon, apr 7 what are loops used for in programming? what are at least 2 different kinds of...
TRANSCRIPT
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 SCIENCE
CYCLE 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 STRUCTURE
if (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 - STRUCTURE
while (condition)
{
//statements
//counter/environment change
}
WHILE LOOPS - STRUCTURE
while (condition)
{
//statements
//counter/environment change
}
Statements – the tasks you want repeated
Counter 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 NUMBER
int number = 1;
int stop = console.nextInt();
while (number <= stop)
{
System.out.println(number);
number++;
}
EXAMPLE C: PRINT 10 MULTIPLES OF AN INPUTTED NUMBER
int multiple = 1;
int number = console.nextInt();
while (multiple <= 10)
{
System.out.println(number*multiple);
multiple++;
}
WARM-UP: APR 8
Write 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 9
Correct 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 NUMBER
int 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 - STRUCTURE
for (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 WHILE
WHILE
int i=0;
while (i < 100)
{
System.out.print(i);
i++;
}
FOR
for (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!