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Lecture 7
Review
• Homework 1 (sample solution)
• Project 1 will be assigned next week
– Draw a picture (whatever you want)in the world by using turtles
e,g,.
http://www.cs.umb.edu/cs110/projects/1/gallery/
http://www.cs.umb.edu/cs110/projects/2/gallery/
Review (Loops)
• Repetition statements allow us to runa statement or a block of statements multiple times
• Often we call them as loops
• for
• while
• do
Example of for Loop
public class Turtle{
public void drawSquare( int len ) {
for(int i=0; i < 4; i++) { forward( len );
turnRight(); }
} }
Repeat thesestatements
4 times
Count starts from 0Add one for each repeat
4 is not included
Example of for Loop
public class Turtle{
public void printNumber( int num ) {
for(int i=0; i < 10; i++) {
System.out.pritnln( num ); }
} }
You can specify the printednumber when you use
this method
Exercise 1 in lecture 6public class Test{ public static void main(String[]
args) { World w = new World();
Turtle t = new Turtle(w);
for(int k=0; k < 10; k++)
{ t.drawSquare(100); t.turn(20);}
}}
public class Turtle{
public void drawSquare(int len){
for(int k=0; k < 4; k++)
{ forward(len); turnRight();}
}}
Exercise 1 in lecture 6 (Another way)public class Test{ public static void main(String[]
args) { World w = new World();
Turtle t = new Turtle(w);
t.drawPicture();
}}
public class Turtle{
public void drawPicture() {
for(int k=0; k < 10; k++)
{ drawSquare(100); turn(20);}
}
public void drawSquare(int len){
for(int k=0; k < 4; k++){ forward(len); turnRight();}
}}
Today’s topic
• More on Arithmetic Expression
- Expression
- Operators
- Precedence
- Math class
Data type
– Integer: { …, -1, 0, 1, … }
e.g. int total;
int number = 5;
– Double: { …, -1, …, -0.5, …, 0, …, 0.5, …, 1, … }
e.g. double average;
double radius = 2.4;
Expressions
• An expression is a combination of one or more operators and operands
Addition +Subtraction -Multiplication *Division /Remainder %
3 + 4
4 / 2
2.3 * 5
operators operands
Assignment
• The result of expression is assigned toa variable by using = symbol
x = 5 + 3;
int x; Variable declaration
Assignment
Note: Somewhat different from math
Variable x contains a value of 8
Assignment (integer)
• If both operands are integers, the result is an integer
5 + 7
int result;result = 5 + 7;
int a = 5;int b = 7;int c;c = a + b;
result = ?
c = ?
Assignment (double)
• If both operands are double (floating point), the result is a double
5.7 + 2.5
double result;result = 5.7 + 2.5;
double a = 5.7;double b = 2.5;double c;c = a + b;
result = ?
c = ?
Division and Remainder
• If both operands to the division operator (/) are integers, the result is an integer (the fractional part is discarded)
• The remainder operator (%) returns the remainder after division
14 / 3 equals8 / 12 equals
40
14 % 3 equals8 % 12 equals
28
Operator Precedence
• Operators can be combined into complex expressions
result = 3 * 5.1 / 2 – 10.1;
• Operators have a precedence which determines the order in which they are evaluated
Operator Precedence
• Multiplication, division, and remainder are evaluated prior to addition and subtraction
result = 3 + 5 * 1;
• Arithmetic operators with the same precedence are evaluated from left to right, but parentheses can be used to force the evaluation order
result = 2 * (3 + 5) * 1;
Examples
• What is the order of evaluation in the following expressions?
a + b + c + d + e1 432
a + b * c - d / e3 241
a / (b + c) - d % e2 341
a / (b * (c + (d - e)))4 123
• You should be careful for this difference
10 2 * 5 = 25
102 * 5
= 1 10 / (2 * 5)
10 / 2 * 5
Math Java
Assignment Revisited
• The assignment operator has a lower precedence than the arithmetic operators
First the expression on the right handside of the = operator is evaluated
Then the result is stored in thevariable on the left hand side
answer = sum / 4 + 10 * number;14 3 2
Assignment Revisited
• The right and left hand sides of an assignment statement can contain the same variable
First, one is added to theoriginal value of count
Then the result is stored back into count(overwriting the original value)
count = count + 1;
Methods of Math class
// return absolute value of num
int abs(int num)
// return value of square root and power
double sqrt(double num)
double pow(double num, double power)
int abs(int num)
This method calculates the absolute of the entered number
How to use?
It takes one integer
| -10 |
The result will be an integer
Class name Method
dot
Math.abs( -10 );
Example
int negative = -10;
int value = Math.abs( negative );
System.out.println( “The result is “ + value);
The result is 10
| -10 |
double sqrt(double num)
This method calculates the square root of the entered number
How to use
Math.sqrt( 6.25 );
It takes one double value or variableThe result will be a double
class name Method
Dot
6.25
Example
double area = 2.25;
double value2 = Math.sqrt( area );
System.out.println( “value2 is “ + value2);
value2 is 1.5
2.25
double pow(double num, double power)
This method calculates the power of the entered number
How to use
Math.pow( 2.0, 3.0 );
It takes two double values or variablesThe result will be a double
Object name Method
Dot
23
Example
int three = 3;double square = Math.pow( three, 2 );double cube = Math.pow( three, 3.0 );
System.out.println( “3 square is “ + square);System.out.println( “3 cube is “ + cube);
3 square is 9.0
3 cube is 27.0
pow method takes two variables32
• Exercise!!!
Exercise 1 (Test.java)
public class Test{
public static void main(String args[]) {
int num1; double num2; num1 = 10 * 5 – 7 / 3; System.out.println( num1 );
num2 = 2.5 * (10.1 -3.7); System.out.println( num2 );
} }
Exercise 1 (Test.java)
public class Test{
public static void main(String args[]) {
int num1; double num2; num1 = 10 * 5 – 7 / 3; System.out.println( “num1 is “ +
num1 );
num2 = 2.5 * (10.1 -3.7); System.out.println( “num2 is “ +
num2 ); }
}
You can print out whatever you wantby using double quotation marks
Exercise 2
Calculate the average score of final exams
e.g.English 90Math 86Science 92History 78Spanish 83
Average ?
Exercise 2 (sample codes)
public class Test{
public static void main(String args[]) {
int num = 5; double average; average = (90+86+92+78+83) / num;
System.out.println( average ); }
}
Is this correct ?
double? = int / int
Exercise 2 (sample codes)
public class Test{
public static void main(String args[]) {
int num = 5; double average, total; total = 90+86+92+78+83; average = total / num;
System.out.println( “Average is “ + average ); }
} Is this correct ?
Exercise 3
Let’s calculate the following equations
(2.3)2 + (3.5)3
How to write in Java program?
Exercise 3 (sample codes)
public class Test{
public static void main(String args[]) {
int num1; double num2; num2 = Math.pow( 2.3, 2 ) +
Math.pow( 3.5, 3 );
System.out.println( “The result is “ + num2 ); }
}
Exercise 4
Let’s solve the following quadratic equations
3X2 = 15
X2 = 15 / 3
X = 5
How to write in Java program?
Exercise 4 (sample codes)
public class Test{
public static void main(String args[]) {
int num1; double num2; num2 = Math.sqrt( 5 );
System.out.println( “3*X^2 = 15“); System.out.println( “X is “ + num2 );
} }
10
10
-10
-10
X
Y
(4,7)
(-6, -2)
Challenge
• Let’s compute the distance between two pointsP1 (4, 7)
P2 (-6, -2)
P1 (X1, Y1)P2 (X2, Y2)
distance = (X1 – X2)2 + (Y1 – Y2)2
10
10
-10
-10
X
Y
(4,7)
(-6, -2)
So, how to compute the distance in Java ???
The result will be double number, let’s store the result into double variable (it should be declared before)
Then print out the distanceTry to report in details like…e.g. The distance between (-1,3) and (2, -1) is 5.0
distance = (X1 – X2)2 + (Y1 – Y2)2
dist = Math.sqrt( Math.pow(X1-X2,2) + Math.pow(Y1-Y2,2) )
public class Test{ public static void main(String[] args) { // declare variables and // assign values into variables representing each point P1 and P2 int x1 = 4; int y1 = 7; int x2 = -6; int y2 = -2; double dist; // caluclate the distance and print out the result dist = Math.sqrt( Math.pow(x1-x2, 2) + Math.pow(y1-y2, 2) );
System.out.println(“The distance between P1(“ + x1 + “,” + y1 +”)” + “ and P2(“ + x2 + “,” + y2 + “) is “ + dist ); }}
Sample codes
