SURVEY OF PROGRAMMING LANGUAGES
UNIT 4
SELECTION
STATEMENT USING PJC (Pascal, Java, C++)
Selection statement
or selection construct or selection structures is also called conditional or
decision statement. The purpose is to make your program select a result from an
option or from a list of options, when a specified condition is met.
4.1 PROGRAMS LAB EXAMPLES
4.1.1 Simple If Statement
In simple if
statement, only a single condition is evaluated, the if-block is executed, if
the condition is true.
Syntax:
Pascal
|
if condition
then //statements |
Java
|
if condition { //statements } |
C++
|
if condition { //statements } |
4.1.2 Lab 1 – program to test the age of a student,
if he eligible to vote
Pascal
|
program lab1; var //declare
variables age : integer; begin //display
action for the user and accept input writeln('Enter your age'); readln(age); //test if age
<18, show 'teenager…’ if (age <18)
then writeln('You are a teenager, you cannot
vote'); end. |
TIP: If you
enter an age value that is from 0-17, the program shows ‘you are a teenager,
you cannot vote‘. However, if you enter a value equal or greater than 18
nothing happens. To advance this program, we will make use of if..then…else
construct. If the condition is false, we use else to specify a new condition to
test.
Java
|
import
java.util.*; public class lab1
{ public static void main(String[] args) { //create scanner object sc (you can
use any variable of your choice) Scanner sc = new Scanner(System. in); System. out. println("Enter your
age:: "); int age = sc.nextInt(); if (age <18) { System.out.println("You are
a teenager, you cannot vote"); } } } |
TIP: You must
wrap the condition within a bracket, else it will show an error
C++
|
#include
<iostream> using namespace
std; int main() { int age; cout<<"Please enter your age::
"; cin >> age; if (age <18) { cout << "You are a
teenager, you cannot vote" <<endl; }
return 0; } |
4.1.3 If…else Statement
In if…else
statement, when the condition of the if-block is evaluated to false, the
statements in the else block, will get executed.
Syntax:
Pascal
|
if condition
then //statements Else //statements |
Java
|
if condition { //statements } else{ //statements } |
C++
|
if condition { //statements } else{ //statements } |
4.1.4 Lab 2 – program to test the age of a student,
if he eligible to vote
Pascal
|
program lab2; var //declare
variables age : integer; begin //display
action for the user and accept input writeln('Enter your age'); readln(age); //test if age
<18, show 'teenager...' if (age
<18) then writeln('You are a teenager, you cannot
vote') else writeln('You are an adult, you can
vote'); end. |
TIP: Any time
you are using if…else, put semicolon in the statement of the last else-block. If
you put semicolon in the statement of the if-block, it will generate error.
Java
|
import
java.util.*; public class lab2
{ public static void main(String[] args) { //create scanner object sc (you can
use any variable of your choice) Scanner sc = new Scanner(System. in); System. out. println("Enter your
age:: "); int age = sc.nextInt(); if (age <18) { System.out.println("You are a
teenager, you cannot vote"); }else{ System.out.println("You are
an adult, you can vote"); }
} } |
TIP: You must
wrap the condition within a bracket, else it will show an error
C++
|
#include
<iostream> using
namespace std; int main() { int age; cout<<"Please enter your age::
"; cin >> age; if (age <18) { cout
<< "You are a teenager, you cannot vote" <<endl; } else{ cout
<< "You are an adult, you can vote" <<endl; }
return 0; } |
4.1.5 If…else…if…else Statement
In if…else…if….else
statement, multiple conditions are evaluated, it is only the block that satisfies
the specified condition that will get executed. You can add as many else-if-blocks
as you want.
Syntax:
Pascal
|
if condition_1
then //statements else if condition_2 then //statements else if condition_3
then //statements else if condition_4 then //statements else //statements |
Java
|
if condition_1
{ //statements } else if condtion_2 { //statements } else if condtion_3 { //statements } else{ //statements } |
C++
|
if condition_1
{ //statements } else if condtion_2 { //statements } else if condtion_3 { //statements } else{ //statements } |
4.1.6 Lab 3 – program to test the classification of
patient’s BMI (Body Mass Index), using the table below.
|
BMI |
CLASSIFICATION |
|
<
18.5 |
Under
weight |
|
18.5
to < 25 |
Normal |
|
25
to < 30 |
Over
weight |
|
>
=30 |
Obesity |
Pascal
|
program lab3; var //declare
variables weight, height, resultBmi : real; begin //display user
action and accept input writeln('Enter weight value in KG:: '); readln(weight); writeln('Enter height value in meters from
(0-2):: '); readln(height); //processing resultBmi := weight / (height * height); //display output writeln('Your body mass index is:: ',
resultBmi:0:2); //test the BMI classification of the patient if resultBmi <18.5 then writeln('Your BMI is Under weight') else if (resultBmi >18.5) and (resultBmi
<25) then writeln('Your BMI is Normal') else if (resultBmi >25) and (resultBmi
<30) then writeln('Your BMI is Over weight') else if resultBmi > 30 then writeln('Your BMI is Obesity') else writeln('Something went wrong'); end. |
TIP: Take note
that we put semicolon in the last else-block. If you put semicolon in the previous
if-block or else-if-block , it will generate error.
Java
|
import
java.util.*; public class lab3
{ public static void main(String[] args) { //create scanner object sc (you can
use any variable of your choice) Scanner sc = new Scanner(System. in); System. out. println("Enter weight
value in KG:: "); double weight = sc.nextDouble(); System. out. println("Enter
height value in meters from (0-2):: "); double height = sc.nextDouble(); double resultBmi = weight / (height *
height); //display output System.out.println("Your body
mass index is:: " + String.format("%.2f", resultBmi)); //test the BMI classification of the
patient if (resultBmi < 18.5) { System.out.println("Your BMI
is Under weight"); }else if ((resultBmi >18.5)
&& (resultBmi <25)) { System.out.println("Your BMI
is Normal"); }else if ((resultBmi >25)
&& (resultBmi <30)) { System.out.println("Your BMI
is Over weight"); }else if (resultBmi > 30) { System.out.println("Your BMI
is Obesity"); }else{
System.out.println("Something went wrong"); } } } |
TIP: You must
wrap the condition within a bracket, else it will show an error. Observe the way
we wrap the two conditions in the else-if-block. Also, we make use of logical
and of java (&&)
C++
|
#include
<iostream> using
namespace std; int main() { float weight, height, resultBmi; cout<<"Enter weight value::
"; cin >> weight; cout<<"Enter height value::
"; cin >> height; resultBmi = weight / (height * height); //display output cout << "Your body mass index
is:: "; printf("%.2f",
resultBmi); //test the BMI classification of
the patient if (resultBmi < 18.5) { cout << "Your BMI is
Under weight " << endl; }else if ((resultBmi >18.5)
&& (resultBmi <25)) { cout << "Your BMI is
Normal " << endl; }else if ((resultBmi >25)
&& (resultBmi <30)) { cout << "Your BMI is Over
weight " << endl; }else if (resultBmi > 30) { cout << "Your BMI is
Obesity " << endl; }else{ cout <<"Something went
wrong"; } return 0; } |
4.1.7 Lab 4 – program for a user to select his/her
gender (take/read/accept character input from the user), using the table below.
|
value |
CLASSIFICATION |
|
m |
Male |
|
f |
Female |
|
When
the user enters something else |
Something
went wrong |
TIP: We will use
the equality operator and the OR operator. Java and C++ OR operator use two
vertical lines | |.
|
Operator |
Pascal |
Java |
C++ |
|
OR |
Or |
|
| |
|
| |
|
Equality
for char and integer in Pascal, while char, int, double in Java and C++ |
= |
= = |
= = |
|
Equality
for String datatype |
|
.equals() |
|
Pascal
|
program lab4; var //declare
variables gender : char; begin //display user
action and accept input writeln('Enter m/f to select your gender'); readln(gender); //test the classification of the user if (gender = 'm') or (gender = 'M') then writeln('Male') else if (gender = 'f') or (gender = 'F') then writeln('Female') else writeln('Something went wrong'); end. |
Java
|
import
java.util.*; public class lab4a
{ public static void main(String[] args) { //create scanner object sc (you can
use any variable of your choice) Scanner sc = new Scanner(System. in); System. out. println("Enter m/f
to select your gender:: "); char gender = sc.next().charAt(0); //test if ((gender=='m') || (gender=='M')) {
System.out.println("Male"); }else if ((gender=='f') ||
(gender=='F')) {
System.out.println("Female"); }else{
System.out.println("Something went wrong"); } } } |
|
TIP: In the
above program, we surround the value m with single quotes |
|
//if you use String
datatype import
java.util.*; public class lab4b
{ public static void main(String[] args) { //create scanner object sc (you can
use any variable of your choice) Scanner sc = new Scanner(System. in); System. out. println("Enter m/f
to select your gender:: "); String gender = sc.next(); //test if (gender.equals("m") ||
gender.equals("M")) {
System.out.println("Male"); }else if
(gender.equals("f") || gender.equals("F")) {
System.out.println("Female"); }else{ System.out.println("Something went
wrong"); } } } |
|
TIP: In the
above program, we surround the value m with double quotes |
C++
|
#include
<iostream> using
namespace std; int main() { char gender; cout<<"Enter m/f to select
your gender:: "; cin >> gender; //test the classification if ((gender == 'm') || (gender ==
'M')) { cout << "Male"
<< endl; }else if ((gender == 'f') || (gender
== 'F')) { cout << "Female"
<< endl; }else{ cout <<"Something went
wrong"; } return 0; } |
|
TIP: Take note
of how we wrap the conditions into parentheses. |
4.1.8 Switch Case Statement
Switch case
statement is a simplified version of if…else…if…else statement, it helps to
make the program to be more readable. Here, only a single condition is evaluated
among several alternatives, the block the meets the condition is executed.
Syntax:
Pascal
|
case
(expression) of label_1 : Statement_1; label_2 : Statement_2; label_3 : Statement_3; else //statements end; |
TIP: The label
represent the condition to be evaluated, you can add as many labels as you
want.
Java
|
switch(expression)
{ case label_1: // statements break; case label_2: // statements break; default: // statements } |
|
TIP: In the
above syntax, we make use of the keyword case, break and default (which does
the job of else) |
C++
|
switch(expression)
{ case label_1: // statements break; case label_2: // statements break; default: // statements } |
4.1.9 Lab 5 – program to test a user gender. Modification
of Lab4 program example
Pascal
|
program lab5; var //declare
variables gender: char; begin //display user action and accept input writeln('Enter m/f to select your gender'); readln(gender); case (gender) of //test the classification of the user 'm' : writeln('Male'); 'M' : writeln('Male'); 'f' : writeln('Female'); 'F' : writeln('Female'); else writeln('Something went wrong'); end;
writeln('Your gender is ', gender ); end. |
|
//this also
works, by separating the labels with comma //test the
classification of the user 'm', 'M' : writeln('Male'); 'f', 'F' : writeln('Female'); |
|
//code snippet
to test for student grade within score range //score is a
variable Case (score)
of 90..100
: WriteLn ('Grade is A'); 80..89 : WriteLn ('Grade is B'); else WriteLn ('You had a carry over'); end; |
Java
|
import
java.util.*; public class lab5
{ public static void main(String[] args) { //create scanner object sc (you can
use any variable of your choice) Scanner sc = new Scanner(System. in); System. out. println("Enter m/f
to select your gender:: "); char gender = sc.next().charAt(0); //test switch(gender) { case 'm':
System.out.println("Male"); break; case 'M':
System.out.println("Male"); break; case 'f': System.out.println("Female"); break; case 'F': System.out.println("Female"); break; default:
System.out.println("Something went wrong"); } } } |
|
//this also
works, by writing the labels on separate line with their own colon (:) //this allows
two or more labels to share statements //test the
classification of the user case 'M': case 'm':
System.out.println("Male"); break; |
C++
|
#include
<iostream> using
namespace std; int main() { char gender; cout<<"Enter m/f to select
your gender:: "; cin >> gender; //test the user classification switch(gender) { case 'm': cout << "Male"
<< endl; break; case 'M': cout << "Male"
<< endl; break; case 'f': cout <<
"Female" << endl; break; case 'F': cout <<
"Female" << endl; break; default: cout << "Something
went wrong"; }
return 0; } |
|
//this also
works, by writing the labels on separate line with their own colon (:) //this allows
two or more labels to share statements //test the
classification of the user case 'M': case 'm': cout << "Male"
<< endl; |
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