204111 – Computer and Programming
Section 451
Lab #3 – Conditional Statements
Student ID
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Signature
Sheet’s Owner
Group partner
1. Boolean Expressions
A boolean expression have only two possible values: true and false. In C# , boolean expressions
can be written using one or more of the following symbols:
Relation
=
6=
>
≥
<
≤
C# notation
==
!=
>
>=
<
<=
Example
x == y
x != y
x > y
x >= y
x < y
x <= y
x
x
x
x
x
x
is
is
is
is
is
is
Meaning
equal to y
not equal to y
greater than y
greater than or equal to y
less than y
less than or equal to y
Boolean expressions can be combined or modified to form a more complex expression using
one of the following operators.
• && combines two boolean expressions using the operator AND. For instance, the expression (x>10) &&(x<10) is true when x is between 1 and 10.
• || combines two boolean expressions using the operator OR. For instance, the expression
(x<1) ||(x>10) is true when x is less than 1 or greater than 10.
• ! negates the truth value of a boolean expression. For example, !(x==1) is true when x
is not equal to 1.
Lesson 1.1: Let x, y and z be of type int and ch of type char. Describe the condition
that makes each of the following boolean expressions true
Expression
x > 2
x%2 == 0
(x%5 == 0)
(x%y == 0)
((x%y == 0) && (z%y
ch == ’a’
((ch >= ’a’) && (ch
((ch >= ’A’) && (ch
((ch >= ’0’) && (ch
(ch != ’*’)
!(ch == ’*’)
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Condition to be true
true when x is greater than 2
true when x is an even number
== 0))
<= ’z’))
<= ’Z’))
<= ’9’))
true if ch is a character between ‘0’ and ’9’
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204111 – Computer and Programming
Section 451
2. if and if...else Statements
if statement is a conditional statement that controls whether a specified statement should be
executed, based on the given condition. There are two forms of usage, as follows.
• Form 1: if statement the statement will be executed when the condition is true
if ( condition )
statement ; // execute if condition == true
In C# , a pair of braces ({}) are used to group multiple statements together, which is
useful when we need more than one statement to be executed when the condition is true.
if ( condition )
statement1 ;
statement2 ;
statement3 ;
}
{
// execute if condition == true
// execute if condition == true
// execute if condition == true
• Form 2: if...else statement The statement1 will be executed if the condition is
true. If the condition is false, the statement2 will be executed instead.
if ( condition )
statement1 ; // execute if condition == true
else
statement2 ; // execute if condition == false
Similar to the above, multiple statements can be grouped together using braces ({}).
if ( condition )
statementT1 ;
statementT2 ;
}
else {
statementF1 ;
statementF2 ;
}
{
// execute if condition == true
// execute if condition == true
// execute if condition == false
// execute if condition == false
Example 2.1: Consider the following pseudo-code
if student’s score is greater than or equal to 60
Print "Passed"
otherwise
Print "Failed"
which means “if the student’s score is greater than or equal to 60, show Passed ; otherwise
show Failed.” Using this pseudo-code, we can write code in C# as follows:
if (score >= 60)
Console.WriteLine("Passed");
if (score < 60)
Console.WriteLine("Failed");
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204111 – Computer and Programming
Section 451
or
if (score >= 60)
Console.WriteLine("Passed");
else
Console.WriteLine("Failed");
Example 2.2: A C# program to determine whether the variable N is even or odd
• Using an if statement
1 using System ;
2 class OddOrEvenC {
3
static void Main () {
4
int N ;
5
Console . Write ( " Please input N : " );
6
N = int . Parse ( Console . ReadLine ());
7
if ( N %2 == 0)
8
Console . WriteLine ( " {0} is Even Number " , N ); // true
9
if ( N %2 != 0)
10
Console . WriteLine ( " {0} is Odd Number " , N ); // true
11
}
12 }
• Using an if...else statement
1 using System ;
2 class OddOrEvenC {
3
static void Main () {
4
int N ;
5
Console . Write ( " Please input N : " );
6
N = int . Parse ( Console . ReadLine ());
7
if ( N %2 == 0)
8
Console . WriteLine ( " {0} is Even Number " , N ); // true
9
else
10
Console . WriteLine ( " {0} is Odd Number " , N ); // false
11
}
12 }
Lesson 2.1: Type the following program into SharpDevelop , then answer the questions
1 using System ;
2 class Lab321C {
3
static void Main () {
4
int N ;
5
N = int . Parse ( Console . ReadLine ());
6
if ( N < 0)
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Console . WriteLine ( " Negative Number " );
8
else
9
Console . WriteLine ( " Positive Number " );
10
}
11 }
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204111 – Computer and Programming
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• Give three different values for the variable N to make the program display “Negative
Number”.
• Give three different values for the variable N to make the program display “Positive
Number”.
• If the user enters 0 to the program, what will be the result?
• Modify the program so that it can also display “Zero Number” (in addition to “Positive
Number” and “Negative Number”) if the user enters 0. Write the program in the box
provided below.
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Lesson 2.2: Quadrant indicator
+Y
Q2
Q1
−X
+X
Q4
Q3
−Y
The following incomplete C# program attempts to identify the quadrant of the input (x, y)
coordinates. If the input coordinates happen to be on either X-axis or Y-axis, the program will
display “I don’t know.”
using System ;
class Quadrant {
static void Main () {
Console . Write ( " Enter X : " );
int x = int . Parse ( Console . ReadLine ());
Console . Write ( " Enter Y : " );
int y = int . Parse ( Console . ReadLine ());
if ( ___ ( a ) ___ )
Console . WriteLine ( " ({0} ,{1}) is in Q1 . " ,
if ( ___ ( b ) ___ )
Console . WriteLine ( " ({0} ,{1}) is in Q2 . " ,
if ( ___ ( c ) ___ )
Console . WriteLine ( " ({0} ,{1}) is in Q3 . " ,
if ( ___ ( d ) ___ )
Console . WriteLine ( " ({0} ,{1}) is in Q4 . " ,
if ( ___ ( e ) ___ )
Console . WriteLine ( " I don ’ t know . " );
x , y );
x , y );
x , y );
x , y );
}
}
Sample outputs
Please input X: -50
Please input Y: 10
(-50, 10) is in Q2.
Please input X: 0
Please input Y: 50
I don’t know.
Complete the program above by determining what should be put in the blanks marked (a)-(e).
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204111 – Computer and Programming
Blank
___(a)___
Section 451
Boolean expression
x > 0 && y > 0
___(b)___
___(c)___
___(d)___
___(e)___
Example 2.3: A cellular phone company has a promotion plan for its customers. The air
time fee is calculated as follows
• Each of the first two minutes costs 5 bahts (per minute)
• Each of the remaining minutes costs 2 bahts (per minute)
The program below will take the number of minutes from the user, and computes the total air
time fee.
using System ;
class Cellphone {
static void Main () {
// Step 1: Take the number of minutes input , minutes
Console . Write ( " Enter the number of minutes : " );
int minutes = int . Parse ( Console . ReadLine ());
// Step 2: Split the number of minutes into two parts ,
// the first two and the remaining
int first , remaining ;
if ( minutes > 2) {
// Step 2.1: If the call takes more than two minutes ,
// then the first two minutes is used entirely and the
// remaining is minutes subtracted by two
first = 2;
remaining = minutes - 2;
}
else {
// Step 2.2: If the call takes less than 2 minutes ,
// these minutes are considered part of the first two
first = minutes ;
remaining = 0;
}
// Step 3: Compute the fee based on the number of minutes
// during the first two minutes , and the number of minutes
// after the first two minutes
int fee = ( first *5) + ( remaining *2);
Console . WriteLine ( " The air time fee is {0} bahts . " , fee );
}
}
Sample outputs
Enter the number of minutes: 1
The air time fee is 5 bahts.
Enter the number of minutes: 5
The air time fee is 16 bahts.
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204111 – Computer and Programming
Section 451
3. Nested if Statements
A nested if (or if...else) statement is an if statement that is part of another if statement.
A program written in this form usually deals with multiple conditions. A general form of nested
IFs is as follows:
if (condition1)
statement1;
else if (condition2)
statement2;
else if (condition3)
statement3;
...
...
else
statementN;
From the above, statement1 is executed when condition1 is true. statement2 is executed
when condition1 is false and condition2 is true. statement3 is executed when condition1
and condition2 are false, and condition3 is true. And so on. Therefore, statementN is
executed when none of the conditions in the IF structure is true.
Example 3.1: Using nested IFs Consider a program that will display a student’s grade based
on his/her score, using the grading policy in the table.
Condition
point < 50
50 ≤ point < 60
60 ≤ point < 70
70 ≤ point < 80
point ≥ 80
Result
Grade F
Grade D
Grade C
Grade B
Grade A
A nested IF can be written in C# as follows:
if ( point < 50)
Console . WriteLine ( " Grade
else if ( point < 60)
Console . WriteLine ( " Grade
else if ( point < 70)
Console . WriteLine ( " Grade
else if ( point < 80)
Console . WriteLine ( " Grade
else
Console . WriteLine ( " Grade
Lab #3
F " );
D " );
C " );
B " );
A " );
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204111 – Computer and Programming
Section 451
Lesson 3.1: Body Mass Index (BMI)
The BMI exercise done in class did not give the complete classification. The complete list is
shown below:
BMI
BM I < 18.5
18.5 ≤ BM I < 25
25 ≤ BM I < 30
BM I ≥ 30
Interpretation
Underweight
Normal
Overweight
Obese
Complete the following BMI calculator program by filling in appropriate boolean expressions
in the provided blanks.
using System ;
class BMICalc {
static void Main () {
Console . Write ( " Enter your weight ( in kg ): " );
double w = double . Parse ( Console . ReadLine ());
Console . Write ( " Enter your height ( in m ): " );
double h = double . Parse ( Console . ReadLine ());
double bmi = w /( h * h );
Console . WriteLine ( " Your BMI is {0: f2 }. " , bmi );
if ( ___ ( a ) ___ )
Console . WriteLine ( " You
else if ( ___ ( b ) ___ )
Console . WriteLine ( " You
else if ( ___ ( c ) ___ )
Console . WriteLine ( " You
else
Console . WriteLine ( " You
are underweight . " );
are normal . " );
are overweight . " );
are obese . " );
}
}
Sample outputs:
Enter your weight: 65
Enter your height: 1.75
Your BMI is 21.22.
You are normal.
Enter your weight: 100
Enter your height: 1.60
Your BMI is 39.06.
You are obese.
Blank
___(a)___
Boolean expression
___(b)___
___(c)___
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4. Programming Exercises
Task 1: Integer identifier
Write a C# program to determine whether the input number is an integer. (Hint: Use the
method Math.Round())
Sample outputs:
Please input N: 1.5
1.5 is not an integer.
Please input N: 99
99 is an integer.
Copy the program into the box below:
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204111 Computers and Programming Task 2: Equation Solution Solver Section 451 Write a C# program to compute f(x) according to the following conditions: ⎧2x + 2,
⎪
f (x) = ⎨ 3x 2 ,
⎪ 4 x 3 − 5,
⎩
x ≤ 10
10 < x ≤ 15 x > 15
Sample outputs Please input x: 5 f(5) = 12 Please input x: 12 f(12) = 432 Please input x: 18 f(18) = 23323 Copy the program into the box below: Lab #3 204111 Computers and Programming Task 3: Odd Number Identifier and Summation Computation Section 451 Write a C# program that accepts 5 positive integers. Then, the program identifies and prints out all the odd numbers and the summation of them. Sample outputs: Please input 5 positive integers: 1 2 3 4 5 Odd numbers: 1 3 5 Summation of odd numbers: 9 Please input 5 positive integers: 2 4 6 8 10 Odd numbers: Summation of odd numbers: 0 Copy the program into the box below: Lab #3