Transcript Lab 3

CSI 1390: Introduction to Computers
TA: Tapu Kumar Ghose
Office: STE 5014
Office hours: Thursday 1300 – 1400hrs.
Email: [email protected]
Assignment
 A triangle is said to be right triangle if the square
of the largest side is equal to the sum of the square
of the other two sides. For example, if x, y and z
are three sides of a triangle and x is the largest side,
then the triangle will be a right triangle if
x2 = y2 + z2
 Take three sides of a triangle from the user and
write program to determine whether the triangle
formed by these three sides is a right triangle or
not.
Solutions
 We will be using the method called readInt() of the
Keyboard.java
 In order to do so, we have to compile the Keyboard.java
program
 Save the Keyboard.java program in the bin directory
 Go to the above directory by using command promt by
using the following steps:
 Open command promt and enter the following commands
 cd\
 cd Program Files\Java\jdk1.5.0_12\bin
 To compile the Keyboard.java program enter the following
command
 javac Keyboard.java
Source code
import java.io.*;
class Triangle {
public static void main(String[] args){
int x, y, z;
Keyboard KB = new Keyboard();
System.out.print("Enter the largest side of the triangle: ");
x = KB.readInt();
System.out.print("Enter the second side of the triangle: ");
y = KB.readInt();
System.out.print("Enter the third side of the triangle: ");
z = KB.readInt();
if((x < y) || (x < z)){ // checking for largest side
System.out.println(“Enter the largest side: ”);
x = KB.readInt();
}
if((x * x) == ((y * y) + (z * z))
System.out.print(“This is a right triangle”);
else System.out.print(“Not a right triangle”);
}
}
Loops
 Sometimes we need to repeat a set of statements
 For example: find the sum of all the digits
 The program would look like as follows:
int sum = 0;
sum = sum + 1;
// sum = 0 + 1 = 1
sum = sum + 2;
// sum = 1 + 2 = 3
sum = sum + 3;
// sum = 3 + 3 = 6
………
sum = sum + 9;
// sum = 36 + 9 = 45
System.out.println(sum);
Loops
 Instead of writing similar set of statement, we
use loop
 Three types of loop:
 for
 while
 do-while
for-loop
 The structure of for loop:
for (initialization ; test_condition ; increment){
// body of the loop
}
 the repeated statements are placed in the body of the
loop
 initialization : initialize the counter of the loop
 test_condition: tests whether the counter is within the
limit
 Increment: modifies the counter
for-loop
 The program for finding the sum of all the digits using
for-loop would look like as follows:
class sum{
public static void main (String[] args){
int sum = 0;
for (int i = 0; i < 10; i = i + 1){
sum = sum + i;
}
System.out.println(sum);
}
}
Some useful statements
 x = x + 1 means we are incrementing the value
of x by 1.
 x = x + 1 can be written as x++
 Similarly, x = x -1 can be written as x—
 x = x + 5 can be written as x += 5
 x = x – 10 can be written as x -= 10
 x = x * 7 can be written as x *= 7
 x = x / 9 can be written as x /= 9
while-loop
 The structure of while loop:
while (test_condition){
// body of the loop
}
 the repeated statements are placed in the body of the loop
 test_condition: tests whether the counter is within the limit
 Modification of counter is done inside the body
 Usually, while loop is used when we have NO idea how many times
the loop body will be executed.
 for loop is usually used when we know the number of iteration of
the loop body.
while-loop
 Example: Take integers from user and keep adding them until any
negative number is entered.
Class addition{
public static void main (String[] args){
int x, sum;
x = sum = 0;
Keyboard k = new Keyboard();
while (x >= 0){
x = k.readInt();
sum += x;
}
System.out.println(sum);
}
}
Practice
 Find the sum of the squares of all the even
numbers between 95.
 using a while statement, produce the sum
1+2+3+ ...+n, where a value for n is entered
by the user.