Department of Computer Science
Faculty of Physical Sciences
Ahmadu Bello University, Zaria

COSC 211 : Object Oriented Programming I - LAB05

Objectives:

To gain experience with:

Selection Statement
Iteration

1. Selection Statement

Three types of selection statements.

if statement.

Performs an action, if a condition is true; skips it, if false.
Single-selection statement—selects or ignores a single action (or group of actions).

if…else statement:.

Performs an action if a condition is true and performs a different action if the condition is false.
Double-selection statement—selects between two different actions (or groups of actions).

switch statement:.

Performs one of several actions, based on the value of an expression.
Multiple-selection statement—selects among many different actions (or groups of actions).

if Single-Selection Statement.

Pseudocode: If student’s grade is greater than or equal to 60 Print “Passed”	Java Code: if ( studentGrade >= 60 ) System.out.println( "Passed" );
If the condition is false, the Print statement is ignored, and the next pseudocode statement in order is performed.

if Single-Selection Statement.

Pseudocode: If student’s grade is greater than or equal to 60 Print “Passed” Else Print “Failed”	Java Code: if ( grade >= 60 ) System.out.println( "Passed" ); else System.out.println( "Failed" );
Note that the body of the else is also indented.

Conditional operator (?:)—shorthand if…else.

Ternary operator (takes three operands)

boolean expression ? the value if the boolean expression is true : the value if the boolean expression evaluates to false

System.out.println(studentGrade >= 60 ? "Passed" : "Failed" );

Example 1:

import java.util.Scanner;

public class Tester
{
   public static void main(String [] args)
   {
	int score ;
	char grade;

	Scanner input = new Scanner(System.in);
	System.out.println("Enter your score");
	score = input.nextInt();

        if (score >=90) 
           grade = 'A'; 
        else if (score >=80) 
           grade = 'B'; 
        else if (score >=70) 
           grade = 'C'; 
        else if (score >=60) 
           grade = 'D'; 
        else 
           grade = 'F';

	System.out.println("Your test score is "+ score 
         + ", which is equivalent to the grade " + grade + ".");
   }
}

import java.util.Scanner;

public class Tester
{
   public static void main(String [] args)
   {
	int score ;
	char grade;

	Scanner input = new Scanner(System.in);
	System.out.println("Enter your score");
	score = input.nextInt();

        if (score >=90) 
           grade = 'A'; 
         
        if (score >=80) 
           grade = 'B'; 
         
        if (score >=70) 
           grade = 'C'; 
           
        if (score >=60) 
           grade = 'D'; 
        else    
           grade = 'F';

	System.out.println("Your test score is "+ score 
         + ", which is equivalent to the grade " + grade + ".");
   }
}

Study, run, compile and run the above codes and observe the output

Click for nested if statements

1. Iteration (Repitation)

Three repetition statements (also called looping statements)Perform statements repeatedly while a loop-continuation condition remains true.

while and for statements perform the action(s) in their bodies zero or more times. if the loop-continuation condition is initially false, the body will not execute

The do…while statement performs the action(s) in its body one or more times

3. Assignments

1. (a) Write an application that will prompt user the to enter the first term, common difference, and the number of terms of an arithmetic progression (AP). It should compute the nth term of the series and the sum of the first n terms. Your code should ensure that the number of terms, n, is positive:

[Hint: use Tn=a +(n– 1)d, and Sn = (n/2)(a+Tn), wherea is the first term,n is the number of terms,d is the common difference,Tn is thenth term of the series, andSn is the sum of the firstn terms.]

2. A quadratic equation of the form has roots:

(a) Write a program that efficiently determines the values of the roots (root1 and root2) of the given equation. Assume that all the variables have been declared as type double. Note that the roots are real and distinct, real and equal, or complex according to whether the discriminant (b2 – 4ac) is positive, zero or negative, respectively. ;

Format the output in the following ways (where root1 and root2 are the calculated roots of the equation).

The roots are real and distinct :root1,root2
The roots are real and equal:root1
The roots are complex

(b) Re-write the example 1 above using switch statement

3. Write a program using the followiing pseudocode:

 (a)

 1 Set total to zero
 2 set grade counter to one
 3
 4 While grade counter is less than or equal to zero
 5   Prompt the user to enter the next grade
 6   Input the next grade
 7   Add the grade into the total
 8   Add one to the grade counter
 9	
 10 Set the class avaerage to the total divided by ten
 11 Print the class avarage

 (b)

 1 Initialize total to zero
 2 Initialize counter to zero
 3
 4 Prompt the user to enter the first grade
 5 Input the first grade (possibly the sentinel)
 6
 7 While the user has not yet entered the sentinel
 8   Add this grade into the running total
 9   Add one to the grade counter
 10  Prompt user to enter the next grade
 11  Input the next grade (Possibly the sentinal)
 12	
 13 If the counter is not equal to zero
 14  Set the average to the total divided by the counter
 15  Print the average
 16 else
 17  Print "No grades were entered!"

 (c)

 1 Initialize passes to zero
 2 Initialize failures to zero
 3 Initialize student counter to one
 4
 5 While student counter is less than or equal to 10
 6   Prompt the user to enter the exam result
 7   Input the next exam result
 8  
 9   If the student passed
 10   Add one to passes
 11  Else 
 12   Add one to failures
 13		
 14  Add one to student counter
 15	 
 16 Print the number of passes
 17 Print the number of failures
 18
 19 If more than eight students passed
 20	 Print "Execellent to instructor"

4. Home Work

1. The value of an investment of P naira after t years at an interest rate ofr% compounded yearly is given by P(1 +r/100)^t.
Write a program that will ask the user to input P,t and r, and will calculate and display the value of the investment.
This should be done in asentinel-controlled loop so that many such calculations can be performed.

2. The first term of aGP is 1.5, and its common ratio is 2. Write a program that will calculate the sum of ten terms. Do not use a formula.