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College of Engineering

Dept. of Computer Science & Eng’g

Computer Programming -

GENG106 - Lab Handbook

Spring 2013 Semester

Lab4: More on Selection

Objectives

At the end of this lab, you should be able to

Use the switch statement.

Use the ternary operator (the conditional expression).

Work more with nested if statements.

Convert nested if statements to switch statements.

Quick Review

switch-statement syntax:

Note:

The selector is an integral constant (i.e. char or one of the integer types).

The default part of the switch is optional.

The break statement is very important. If omitted, then the current case and the following

cases will all execute, which is not usually the required logic. In some occasions, however,

we may want to execute a statement if more than one case of the selector is satisfied. In such

occasions we omit the statement and the break from all the cases for which this statement

must be executed, and leave it for the last one (see exercise 2).

The ternary operator:

Note:

The ternary operator can be used to replace an if/else statement.

The value assigned to variable depends on the condition.

The value if true / value if false could be an expression or an input

command. The data type, however, must be compatible with that of variable.

variable = condition ? value if true : value if false ;

switch (selector)

{

case label1: statement1;

break;

case label2: statement2;

break;

...

case labeln: statementn;

break;

default: statementd; // optional

break;

}

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1) The following program is a demonstration for using the switch statement.

#include <iostream>

#include <string>

using namespace std;

int main()

{

int yearCode;

string yearName;

cout << "Please enter the number of a class year (1-5) : ";

cin >> yearCode;

switch (yearCode)

{

case 1:

yearName ="Freshman";

break;

case 2:

yearName = "Sophomore";

break;

case 3:

yearName = "Junior";

break;

case 4:

yearName = "Senior";

break;

case 5:

yearName = "Graduate";

break;

default:

cout << "YearName: code error: " << yearCode << endl;

yearName = "";

}

cout << yearName << endl;

return 0;

}

Your Answer:

Run the program and write down the output when 1 is entered; when 3 is entered; and when 9 is

entered.

___________________________________________________________________

___________________________________________________________________

Modify the above program by commenting out the break statements in case 1, case 2, … case 5

(i.e. by typing // before the keyword break). What is output by the program when 2 is entered and

when 4 is entered?

___________________________________________________________________

___________________________________________________________________

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1) Write an interactive program that asks the user to enter the first letter of a geometric shape, and then

let your program calculate and output the and of the chosen shape. For simplicity,

let your program deal only with rectangles and circles.

Hints:

For a rectangle: , ))

For a circle: where is the radius.

Your program must display an error message to indicate that the user entered a character

other than ’R’, ’r’, ’C’ or ’c’.

Use the switch statement to decide which formulas to be used.

2) In Question #3 of Lab-3 you were asked to use the if/else statement to code the following function.

Complete the following ternary operator to calculate

= ? ____________________ : _______________________;

Now, make a new copy of your solution to Q3 of Lab-3 and then replace the if/else statement (in the

copy) with the above ternary operation.

Which one of the two programs has fewer lines? __________________

3) Complete the following statement that determines the number of days in February based on the

Boolean variable leap of Question #2 (Lab-3):

= ? 29 : 28;

Modify your program to use this statement instead of the if/else statement.

4) Write a C++ program that asks the user to input the wattage (or watts) of a standard light bulb and

uses a switch statement to assign to the variable lumens the expected brightness. Use this table:

Watts Brightness (lumens)

15 125

25 215

40 500

60 880

75 1000

100 1675

Assign the value -1 to lumens if the value of watts is not in the table.

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5) Convert the following nested if statement to a switch statement and then use it in a program that asks

the user for the integer value choice and print the correct message.

if (choice == 1) cout << “You have chosen one”;

else if (choice == 2)

cout << “You have chosen two”;

else if (choice == 3)

cout << “You have chosen three”;

else if (choice == 4)

cout << “You have chosen four”;

else

cout << “Invalid choice\n”;

6) The table below shows the normal boiling points of several substances. Write a program that

prompts the user for the observed boiling point of a substance in °C and identifies the substance if

the observed boiling point is within 5% of the expected boiling point. If the data input is more than

5% higher or lower than any of the boiling points in the table, the program should output the

message “Substance unknown”.

Substance Normal boiling point(°C)

Water 100

Mercury 357

Copper 1187

Silver 2193

Gold 2660

7) Modify the program of Question#5 (Lab-3) to comply with the conditions given in the following

table:

pH Range Solution is

pH<3 very acidic

3<pH<7 Acidic

pH=7 Neutral

7<pH<12 Alkaline

pH>12 very alkaline

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8) Isaac Newton discovered that a glass prism can split white light apart into its constituent colors.

Wavelengths of visible light fall approximately into the range 400 – 700 nm (nm = nano-meter =

10-9

meter).

The table below shows the relationship between wavelength and color.

Color Wavelength range (nm)

Violet 400 - 424

Blue

424 - 491

Green

491 - 575

Yellow

575 - 585

Orange

585 - 647

Red

647 - 700

Write a C++ program that inputs a wavelength and then displays the associated light color. If the

wavelength is shorter than 400 nm or longer than 700 nm, display the message “Wavelength

outside visual range”. Classify boundary wavelengths as the lower-wavelength color. For

example, label a wavelength of 424 nm as violet.