10-Lec - Nested IF Statement.pptx

CONDITIONAL
STATEMENTS
NESTED IF STATEMENTS

NESTED IF
STATEMENTS
We can have two or more if statements inside each other to
check multiple conditions
 These are called nested if statements
Nested if statements can be used to test more than one
condition
Use indentation to reflect nesting and aid readability
 Typically indent 3-4 spaces or one tab
Need to take care when matching up { } brackets
 This way you can decipher the nesting of conditions
2

NESTED IF
STATEMENTS
if ( logical expression1 )
{
if ( logical expression2 )
{
// Statements to execute if expressions1 and expression2 are true
}
else
{
// Statements to execute if expression1 true and expression2 false
}
}
else
{
// Statements to execute if expression1 false
}
3

FLOWCHART FOR A
NESTED IF STATEMENT
4

NESTED IF CODE
// Determine loan qualification
if (employed == ‘y’)
{
if (recentGrad == ‘y’)
{
cout << “You qualify!”
}
}
Note: this could be done with one if and two conditions.
5

NESTED IF CODE
// Determine loan qualification using one if and
//two conditions
if (employed == ‘y’ && recentGrad == ‘y’)
{
cout << “You qualify!”
}
6

NESTED IF
STATEMENTS
// Simple nested if example
cin >> a >> b;
if (a < b)
{
cout << “A is smaller than Bn”;
if ((a > 0) && (b > 0))
cout << “A and B are both positiven”;
else
cout << “A or B or both are negativen”;
}
7

NESTED IF
STATEMENTS
// Ugly nested if example
if (a > 0) {
if (b < 0) {
a = 3 * b;
c = a + b; } }
else {
a = 2 * a;
c = b / a; }
 It is hard to see what condition the else code goes with
8

NESTED IF
STATEMENTS
// Pretty nested if example
if (a > 0)
{
if (b < 0)
{
a = 3 * b;
c = a + b;
}
}
else
{
a = 2 * a;
c = b / a;
}
9

BOOLEAN VARIABLES
 In C++ we can store true/false values in Boolean variables
 The constants “true” and “false” can be used to initialize
these variables
 bool Done = true;
 bool Quit = false;
 Boolean expressions can also be used to initialize these
variables
 bool Positive = (a >= 0);
 bool Negative = (b < 0);
10

BOOLEAN VARIABLES
 Boolean variables and true/false constants can also be
used in logical expressions
 (Done == true) is true
 (Quit != true) is true
 (Done == Quit) is false
 (true == Positive) is true
 ((a < b) == false) is false
 (Negative) is false
11

BOOLEAN VARIABLES
 Internally C++ stores Boolean variables as integers
 0 is normally used for false
 1 is normally used for true
 Any non-zero value is also considered true
 It is considered “bad programming style” to use integers
instead of true/false
 bool Good = 0;
 bool Bad = 1;
 bool Ugly = a;
12

BOOLEAN VARIABLES
 Integers are used when writing Boolean values
 cout << Good will print 0
 cout << Bad will print 1
 cout << Ugly will also print 1
 Integers are also used when reading Boolean values
 cin >> Good;
 Entering 0 sets Good variable to false
 Entering any value >= 1 sets Good variable to true
 Entering value < 0 also sets Good variable to true
13

PRIME NUMBER
EXAMPLE
 How can we test a number to see if it is prime?
 We are given numerical values between 1..100
 We need to see if it has any factors besides 1 and itself
 We need some nested if statements
 Test if input number is between 1..100
 If so, then test if 2,3,5,7 are factors of input number
 Then print out “prime” or “not prime”
14

PRIME NUMBER
EXAMPLE
// Check for prime numbers using a factoring approach
#include <iostream>
using namespace std;
int main()
{
// Local variable declarations
// Read input parameters
// Check input is valid
// Check if number is prime
// Print output
return 0;
}
15
For the first version
of program we just
write comments in
the main program to
explain our approach

PRIME NUMBER
EXAMPLE
// Check for prime numbers using a factoring approach
#include <iostream>
using namespace std;
int main()
{
// Local variable declarations
int Number = 0;
bool Prime = true;
// Read input parameters
cout << “Enter a number [1..100]:”;
cin >> Number;
16
For the second
version of program
we initialize variables
and read the input
value from user

PRIME NUMBER
EXAMPLE
…
cout << “Enter a number [1..100]:”;
cin >> Number;
// Check input is valid
if ((Number < 1) || (Number > 100))
cout << “Error: Number is out of rangen”;
else
{
// Print output
}
17
For the next version
of the program we
add code to verify the
range of input value

PRIME NUMBER
EXAMPLE
…
if (Number == 1) Prime = false;
if ((Number > 2) && (Number % 2 == 0)) Prime = false;
// Print output
if (Prime)
cout << “Number “ << Number << “ IS primen”;
else
cout << “Number “ << Number << “ is NOT primen”;
… 18
In the final
version we finish
the prime number
calculation and
print the output

PRIME NUMBER
EXAMPLE
 How should we test the prime number program?
 Test the range checking code by entering values “on the
border” of the input range (e.g. 0,1,2 and 99,100,101)
 Test program with several values we know are prime
 Test program with several values we know are not prime
 To be really compulsive we could test all values between
1..100 and compare to known prime numbers
 What is wrong with this program?
 It only works for inputs between 1..100
 It will not “scale up” easily if we extend this input range
19

SUMMARY
 In this section we showed how if statements and if-else
statements can be nested inside each other to create more
complex paths through a program
 We also showed how proper indenting is important to read
and understand programs with nested if statements
 We have seen how Boolean variables can be used to store
true/false values in a program
 Finally, we used an incremental approach to create a
program for checking the factors of input numbers to see
if they are prime or not
20

EXAMPLE: WAGES.CPP
Write a C++ program that calculates weekly wages for hourly
employees.
 Regular hours 0 - 40 are paid at $10/hours.
 Overtime (> 40 hours per week) is paid at 150%

10-Lec - Nested IF Statement.pptx

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