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Try this:
void main() { // 1. declare and initialize variables int counter = 1; // 2. now do the while loop while (counter < 5) { printLine("counter is equal to " + counter); // 3. add 1 to the value of counter counter = counter + 1; } // 4. the while loop has finished, so program continues on to here printLine("Goodbye"); }
What was printed?
Counter is equal to 1 Counter is equal to 2 Counter is equal to 3 Counter is equal to 4 Goodbye
Notes on Above code:
Loops are repeating sets of statements and in the case of the while loop, here is the formula:
while (this statement is true) { // execute the statements or lines between these brackets // add 1 to the counter (usually) } // and continue the program with the following lines
E.g.
while (x <5) { printLine(" x = " + x); x = x + 1; }
What will the above code output?
Java Exercises:
void main() { while (x < 5) { printLine(" x = " + x); // x = x + 1; } }
void main() { count = 0; while (count < 8) { Printline("Count is equal to " count); }
do while loops are similar to while loops except that the condition is tested after the code to be repeated or looped. The general form of a do … while loop is as follows:
do { // execute code between these brackets } while (true or false (boolean) statement)
Note that the repeated code is always executed once, because the condition is tested after the loop ends. It may be better to use a plain old while loop in most cases, because it tests the condition before the loop starts.
E.g.
int y = 10; printLine("Counting Down..."); do { printLine(".. " + y); y = y - 1; } while (y > 1); printLine("Blast Off");
Try it! What did You get?
Java Exericises
void main() { int counter = 10; while (counter > 1) { printLine(" " + counter + " green bottles hanging on the wall"); printLine(" " + counter + " green bottles hanging on the wall"); printLine("And if one green bottle should accidently fall, "); printLine("There'd be " + counter-1 + " green bottles hanging on the wall"); counter = counter - 1; } }
Java for loops are a short hand way of;
All in one statement.
Before we carry on we have have to learn about the:
x++;
is the same as
x = x + 1;
X++ increments (or increases) the value of X by 1. Here is an example that we could use in a while loop:
int x = 0; // declare and initialize counter x while (x < 5) { printLine(" x = " + x); // add 1 to the value of x x++; // same as (x = x + 1) }
Similarly, the:
y– decrements (or decreases) y by 1.
y--;
is the same as
y = y - 1;
Try this:
int y = 10; while (y > 0) { printLine(" and " + y); y--; }
So, back to the for Loop.
A for Loop sets all the conditions of a loop inside the parantheses after the for statement.
Example A.
for (int x = 0; x < 10; x++) { printLine("x = " + x); }
The form of the for loop is:
for (INITIALIZE counter; boolean CONDITION; ITERATION) { // repeated code to be executed. }
Iteration means repetition, or repeating. In actual fact it is either usually increased by 1 (x++) or decreased by 1 ( y–).
In example A above, the Initialisation statement is “int x = 0;”.
This statement declares x as an int and initializes x to be equal to a value of 0 in one go.
The boolean condition is “x < 10;”. This statement tests x and if it is true, then the loop is allowed to execute, If it is false (x=10 or x > 10), then the loop is bypassed and the program execution continues after the { curly brackets } following the for statement.
Example B. Count down from 10 to 1:
for (int x = 10; x>0; x--) { printLine(x); }