1. while loop Condition Statement list
How do I know the condition will become false?
while (mark.isFacingNorth()) {
mark.pickThing();
mark.move(); }
Condition
Statement
list T
while
(mark.getStreet()!=10) {
mark.move(); } F
We should make sure the statement list will work towards the exit condition of the loop. But how?
Drink more coffee!
Think clear!
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2. Variables are name of memory locations where values are stored.
int j;
int i = 1;
j = i;
City ny;
// ny = i; // this is illegal
ny = new City();
Robot mark;
RobotSE tom = new RobotSE(ny,0,0,Direction.EAST);
mark = tom;
// tom = mark; // this is illegal
We have to decide for a variable:
the name
the type
the value
This may be changed later
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3. Variables We can use variable to control a loop.
// the following code will ask the robot to keep moving
// until it picks up 10 things.
RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
int count=0;
while (count != 10) {
if (mark.canPickThing()) {
mark.pickThing();
count ++; }
else {
mark.move();
How do I know the robot eventually will have 10 things?
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4. To guarantee exit, we may provide an upper bound of effort
How about, pick 10 things, if possible, with 100 steps?
RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
int count=0, distance=0;
while (count != 10 && distance < 100) {
if (mark.canPickThing()) {
mark.pickThing();
count ++; }
else {
mark.move();
distance++;
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5. while loop for loop Statement Condition Statement list list
repeat n times
Statement
list
< n F
= n
while (Condition) {
Statement list }
for (???;???;???) {
Statement list }
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6. don’t forget “;” be careful
Another form of loop:
do loop do {
Statement list
} while (condition);
Statement
list
don’t forget “;” be careful
Condition T
This is not uncommon (forget the author’s comments on page 243) F
E.g., ITK’s student has to take ITK168 until he/she gets a C or better.
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7. Another example of using do-loop
Ask the user to input y (yes) or n (no), where y and n are the only two valid inputs for the program to proceed. This way, we avoid a great chance of accidentally pressing the keyboard.
String answer; do {
answer = JOptionPane.showInputDialog(“y or n?”);
} while (!answer.equals(“y”) && !answer.equals(“n”));
String answer;
answer = “x”;
while (!answer.equals(“y”) && !answer.equals(“n”)) {
answer = JOptionPane.showInputDialog(“y or n?”); }
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8. Primality Test A prime number is a positive integer that cannot be
factorized, i.e., no numbers other that 1 and itself
can divide it.
Is (893 % 2 == 0) ?
Is (893 % 3 == 0) ?
Is (893 % 4 == 0) ?
Is (893 % 5 == 0) ?
Is (893 % 6 == 0) ? .
Is (893 % 892 == 0) ?
is 893 a prime?
This test is silly but can do the job!
We can write a loop
to test these.
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9. Primality Test int p,r,i; // r: remainder, i: factor do {
p = Integer.parseInt(
JOptionPane.showInputDialog(“input an number:));
} while (p <= 1);
i=1; do {
i++;
r = p % i; // r is the remainder of p divided by i
} while (i < p && r != 0);
if (i == p)
System.out.println(“a prime number.”);
else
System.out.println(“not a prime number.”);
System.out.println(“The least factor is ”+i); }
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10. The break statement in a loop will force the program to jump out of the loop immediately.
Break a loop
int i = 2; do {
r = p % i;
i++;
} while (i < p && r != 0);
int i = 2; do {
r = p % i;
if (r == 0) break;
i++;
} while (i < p);
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11. Break a loop import javax.swing.JOptionPane; ....
public static void marryAsk() {
String answer;
do {
answer = JOptionPane.showInputDialog(
"Would you marry me? (y/n)");
if (answer.equals("Y") || answer.equals("y"))
"Really? (y/n)");
} while (!answer.equals("Y") && !answer.equals("y"));
JOptionPane.showMessageDialog(null, "Great!!"); }
if (answer.equals("F") || answer.equals("f"))
break;
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12. The Loops with multiple breaking points
....
while (......) {
if (....) break;
..... }
Statement
list
Condition T F
Spaghetti code?
Why spaghetti code is bad?
Well, this is not spaghetti code!
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13. The Loops with multiple breaking points
This is Spaghetti code?
This is not spaghetti code! All paths come to the same point
Multiple-break-loop does not cause the trouble as the spaghetti code does
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14. 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 4 5 6 7 8 9 10 11
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15. Continue in a loop The continue statement in a loop will force the
program to check the loop condition immediately.
RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
while (mark.getAvenue() <= 10) {
if (mark.frontIsClear()) {
mark.move();
continue; }
mark.turnRight();
mark.turnLeft();
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16. Continue in a loop
The continue statement in a loop will force the program to check the loop condition immediately.
String answer;
do {
answer = JOptionPane.showInputDialog(
"Would you marry me? (y/n)");
if (!answer.equals("Y") && !answer.equals("y"))
continue;
JOptionPane.showMessageDialog(null, "Great!!");
break;
} while (true);
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17. Euclid Algorithm: finding the greatest common divisor
int euclidAlgorithm(int a, int b) {
int r = a % b;
while (r != 0)
a = b;
b = r;
r = a % b; }
JOptionPane.showMessageDialog(null,“The GCD is”+b);
return b;
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18. Bottom Factoring RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
if (mark.canPickThing()) {
mark.pickThing();
mark.turnAround();
} else {
mark.putThing(); }
RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
if (mark.canPickThing()) {
mark.pickThing();
} else {
mark.putThing(); }
mark.turnAround();
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19. Top Factoring RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
if (mark.canPickThing()) {
mark.turnAround();
mark.pickThing();
} else {
mark.move(); }
RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
mark.turnAround();
if (mark.canPickThing()) {
mark.pickThing();
} else {
mark.move(); }
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20. Top Factoring RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
if (mark.countThingsInBackpack()>2) {
mark.putThing();
mark.move();
} else {
mark.turnArounde(); }
Top Factoring
RobotSE mark = new RobotSE(ny,0,0,Direction.EAST);
mark.putThing();
if (mark.countThingsInBackpack()>2) {
mark.move();
} else {
mark.turnAround(); }
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21. Top Factoring RobotSE mark = new RobotSE(ny,0,0,....); ...
if (mark.isFacingNorth()) {
mark.turnAround();
mark.pickThing();
} else {
mark.move(); }
RobotSE mark = new RobotSE(ny,0,0,....);
...
mark.turnAround();
if (mark.isFacingNorth()) {
mark.pickThing();
} else {
mark.move(); }
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22. Top Factoring int a=1,i=0; ... if (i==0) { i++; a = a+i; } else {
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