JavaJavaPrepared by Gary Langner

Types of Loops

for loop (entrance controlled)

– do an action for a definite number of times

while loop (entrance controlled

– do an action while a condition is true do…..while (exit controlled)

– do an action until a condition is true

Boolean Operators= = Is equal to

< Is less than

> Is greater than

<= Is less than orequal to

>= Is grater than orequal to

!= Is not equal to

|| Or

&& And

! Not

For Loop (with single statement)

For (<Initialization expression>;< termination condition>; <update expression>)

for (i = 1; i <= 10; i++)

System.out.println(i);

1 <---------------------------Output2345678910

No semicolon!

No braces “{“ on single statement

For Loop (with multiple statement)

Int amt, num,total1=0, total2=0;

for (int j=1; j <= 10; j++){ //begin for loop amt = SavitchIn.readInt(); // or Scanner class num = SavitchIn.readInt(); total1+= amt; //accumulator statement adds up all amt and stores answer in total1 total2+= num; //accumulator statement adds up all num and stores answer in total2

System.out.println( “The number is” + EasyFroamt.format (num,6));} //end for loop

Note: the indenting for readability

Note: the bracket alignment

Loop Body

For Loop (downward counting loop)

for (int k = 20; k >= 15; --k)

System.out.print( “K = “+EasyFormat.format (k,9);

For Loop (counting by more than one)

int sum = 0;

//add the EVEN numbers 2-10

for (int j = 2; j <=10; j += 2)

sum+ = j;

System.out.println(“sum “)

For Loop (style tips)

//loop limits can be defined as constants or as variables and //then have assigned values

final int LOOPLIMIT = 500;

int lcv; //allows reuse in the program

for (lcv = 1; lcv <= LOOKLIMIT; lcv++)

//loop body

int loopLimit;

loopLimit=SavitchIn.readInt()OR

While Loop

While (boolean expression)

loop statement;

Entrance controlled (pretest)

While <Boolean expression>

Statements after loop

Loop BodyTrue

False

While LoopOften used for sentinel value (terminal value)

The boolean expression MUST have a value prior to the loop

Loop control variable must change IN THE loop and become TRUE (otherwise infinite loop)

power2 = 1;while (power2 < 100){ //begin loop

System.out.println( power2);power2*=2;} //end loop

see next page

No semicolon

Multiplies power2 by 2 with each iteration

While Loop (sentinel value)

int numscores = 0;int sum = 0;int score;System.out.print( “Enter a score (-999 to quit) ”);int score = SavitchIn.readInt(); //or scanner classwhile (score != -999){

numscores++; //simple counter (counts by 1’s)sum += score; //adds up all scores and stores in sumSystem.out.print( “Enter a score (-999 to quit) ”);score=SavitchIn.readInt() //or scanner class

} //end whileSystem.out.print(“sum of scores= “) + sum);

Double Prompt and input required

While Loop (compound conditions)

int a=SavitchIn.readInt();

int b=SavitchIn.readInt();

while ((a > 0) && (b>0))

{

statements;

} //end while

Do Loop Post test or entrance controled loop

Do body of loop

While<boolean

expression>

True

False

Do LoopUsed when it is necessary to loop at least once.

The boolean expression MUST have a value before it is used at the end of the loop.

Loop control variable must change IN THE loop and become FALSE (otherwise infinite loop)

Generally used less frequently except for data validation.

j=0;do{

j+=2;System.out.println( j);

} while (j != 5);

No semicolon

next pg

BAD! j must become five for loop to terminate. This is infinite—Must Ctl Alt Del to stop

Nested Loops

for (int k = 1; k <=5; ++k){ for (int j = 1; j <=3; ++j)

System.out.print(EasyFormat.format((k+j),4));System.out.println();;

} //end for loop2 3 4

3 4 54 5 65 6 76 7 8

output

Loops-writing style Each loop should have its own level of indenting. The { and } should start in the same column Comments should describe what a loop does.

(place inside of loop) Comments should be used at end of loop i.e..

//end of for loop Isolate loops by skipping a line before and after

the loop.

Now on to some programming practice...

Go back to the assignments page and download the first looping program. Good Luck!