CS 101 Computer Programming

StatementsReview++

Reviewed so far..• Variables• Constants• Order of Execution• Boolean expressions and variables• if statements, if-else statements• nested if statements• loops: while statements, for statements• Nested loops

CS 101 | Özyeğin University 2

int x = 10;

private static final int SIZE = 50;

boolean withinLimits = true;

if(x < 0 || x > 100) {withinLimits = false;

}

while(x < 100) {...while(y < 100) {

...}

}

Exercise

CS 101 | Özyeğin University

import acm.program.*;

public class ExecutionOrder extends ConsoleProgram {

public void run() { int x = 10; /* 1 */ while(x < LIMIT) { /* 2 */ if(x%2 != 0) { /* 3 */ x += 3; /* 4 */ } else {

x *= 10; /* 5 */}

} }

private static final int LIMIT = 100; /* 6 */}

What is the order of execution? What is the value of x at the end?

Nested Loops

CS 101 | Özyeğin University

i:0,j:3 – i:0,j:2 – i:0,j:1 – i:1,j:3 – i:1,j:2 – i:1,j:1 – i:2,j:3 – i:2,j:2 – i:2,j:1 –

import acm.program.*;

public class Stars extends ConsoleProgram {

public void run() {for(int i = 0; i < N; i++){

for(int j = N; j > 0; j--){ print("i:" + i + ",j:" + j + " - ");}

} }

private static final int N = 3;}

Exercise

CS 101 | Özyeğin University

Write a ConsoleProgram that outputs N rows of stars in the format shown belowimport acm.program.*;

public class Stars extends ConsoleProgram {

public void run() {

/* TODO */ }

}

Exercise

CS 101 | Özyeğin University

Write a ConsoleProgram that outputs N rows of stars in the format shown belowimport acm.program.*;

public class Stars extends ConsoleProgram {

public void run() {for (int i = 0; i < 10; i++) {

for (int j = 0; j <= i; j++) {print("*");

}println("");

} }

}

Exercise

CS 101 | Özyeğin University

Now modify the program to print out rows of stars in the format shown belowimport acm.program.*;

public class Stars extends ConsoleProgram {

public void run() {

/* TODO */ }

}

Exercise

CS 101 | Özyeğin University

Now modify the program to print out rows of stars in the format shown belowimport acm.program.*;

public class Stars extends ConsoleProgram {

public void run() {for (int i = 0; i < 10; i++) {

for (int j = 0; j < 10-i ; j++) {print("*");

}println("");

} }

}

Exercise

• Write a Java program that reads N positive integers and prints the maximum of those.

Exercise

• Write a Java program that reads integers from the users as long as they are positive, and finally prints the maximum of the numbers.

public class MaxOfIntegerList extends ConsoleProgram { public void run() { println("This program reads positive integers,"); println("and prints the maximum."); println("The program exits when the user enters a non-positive value."); int maximum = 0; while(true) { int value = readInt("Enter > "); if(value <= 0) break; if(value > maximum) { maximum = value; } } if(maximum == 0) { println("You did not enter any positive integers."); } else { println("Maximum is " + maximum); } }

private static final int N = 5; }

Exercise

• Write a Java program that reads N positive integers and prints the maximum two of those.

public void run() { println("This program reads " + N + " *positive* integers,"); println("and prints the *two* maximum."); int maximum = 0; int secondMaximum = 0; for(int i=0; i < N; i++) { int value = readInt("Enter > "); if(value <= 0) { println("Please enter a POSITIVE integer!"); i--; // Decrement i so that we read the number again. } else if(value > maximum) { secondMaximum = maximum; maximum = value; } else if(value > secondMaximum) { secondMaximum = value; } } println("Maximum is " + maximum); println("Second maximum is " + secondMaximum);}

Exercise

• Write a Java program that helps me decide how to travel.– If I'll travel for less than 1 km, I'll walk in any condition.– If I'll travel for less than 5 km, biking is my priority.– If I'll travel for more than 500 km, I'll fly in any condition.– I can ride my bike if the temperature is between 8 and 28

degrees.– I'll drive my car otherwise.

• Try to use as few boolean conditions as possible, and with exactly 4 println()’s.

Exercise• Implement the Checkerboard example using a single

loop (instead of the nested loop).

Exercise• Implement a graphical Java program in which a ball

continuously scrolls from left to right.

public class ScrollingBall extends GraphicsProgram{ // Named constants can be defined at the top or the bottom of the class. private static final int BALL_SIZE = 50; private static final int PAUSE_TIME = 50;

public void run() { GOval ball = new GOval((getWidth()-BALL_SIZE)/2, (getHeight()-BALL_SIZE)/2, BALL_SIZE, BALL_SIZE); ball.setFilled(true); ball.setFillColor(Color.RED); add(ball); int dx = 10;

while(true) { // forever running! ball.move(dx, 0);

if(ball.getX() > getWidth()) ball.setLocation(0, ball.getY()); pause(PAUSE_TIME); } }

public void init() { setSize(500,300); }}