1. Programming Fundamentals
Lecture 6
Ms. Farah Younas

2. Agenda of Lecture The if Selection The if/Else Selection
Nested if/else Selection

3. Relational Operators

4. Relational Operators

5. Relational Operators

6. Confusing Equality (==) and Assignment (=) Operators
Dangerous error
Does not ordinarily cause syntax errors
Any expression that produces a value can be used in control structures
Nonzero values are true, zero values are false
Example using ==:
if ( payCode == 4 )
cout<<"You get a bonus!\n";
Checks paycode, if it is 4 then a bonus is awarded
Example, replacing == with =:
if ( payCode = 4 )
cout<<"You get a bonus!\n" ;
This sets paycode to 4
4 is nonzero, so expression is true, and bonus awarded no matter what the paycode was
Logic error, not a syntax error

7. The Logical Operators && ( logical AND ) || ( logical OR )
Returns true if both conditions are true
|| ( logical OR )
Returns true if either of its conditions are true
! ( logical NOT, logical negation )
Reverses the truth/falsity of its condition
Unary operator, has one operand
Useful as conditions in loops
Expression Result
true && false false true || false true
!false true

8. Decision Making in C++
Decision making is about deciding the order of execution of statements based on certain conditions or repeat a group of statements until certain specified conditions are met.
C++ handles decision-making by supporting the following statements,
If statement
switch statement
conditional operator statement
goto statement

9. Decision Making with If statement
The if statement may be implemented in different forms depending on the complexity of conditions to be tested. The different forms are:
Simple if statement
If…else statement
Nested if…else statement
else if statement

10. Simple If statement The general form of a simple if statement is,
If (expression) {
Statement-inside; }
Statement-outside;
If expression is true, then statement-inside is executed, other wise only statement- outside will be executed.

11. Simple If statement The general form of a simple if statement is,
If (expression) {
Statement-inside; }
Statement-outside;
If expression is true, then statement-inside is executed, other wise only statement- outside will be executed.

13. The if Selection Structure
Used to choose among alternative courses of action
Pseudocode:
If student’s grade is greater than or equal to 60 Print “Passed”
If condition true
Print statement executed and program goes on to next statement
If false, print statement is ignored and the program goes onto the next statement
Indenting makes programs easier to read
C++ ignores whitespace characters

14. The if Selection Structure
Pseudocode statement in C++:
If grade >= 60
Print “Passed”
if ( grade >= 60 ) cout<<"Passed\n";
C++ code corresponds closely to the pseudocode
Diamond symbol (decision symbol)
Indicates decision is to be made
Contains an expression that can be true or false
Test the condition, follow appropriate path

15. The if Selection Structure

16. The if Selection Structure
if structure is a single-entry/single-exit structure
true
false
grade >= 60
print “Passed”
A decision can be made on any expression.
zero - false
nonzero – true
Example:
3 - 4 is true

17. Simple If statement - Example

18. Simple If statement - Example
#include<iostream.h>
int main() {
int x,y;
x=15;
y=13;
If(x > y)
cout<<“x is greater than y”; }
return 0;

19. The if/else Selection Structure
Test for multiple cases by placing if/else selection structures inside if/else selection structures

20. The if/else Selection Structure
Pseudocode:
If student’s grade is greater than or equal to 60
Print “Passed”
Else
Print “Failed”
C++ code:
if ( grade >= 60 )
cout <<"Passed\n";
else
cout << "Failed\n";
Ternary conditional operator (?:)
cout << ( grade >= 60 ? "Passed" : "Failed" );
grade >= 60 ? cout << "Passed" : cout << "Failed";

21. The if/else Selection Structure
The general form of a simple if/else statement is,
If (expression) {
Statement-block1; }
else
Statement-block2;
If expression is true, then statement-block1 is executed, other wise only statement- block2 will be executed.

22. The if/else Selection -Example
#include<iostream.h>
int main() {
int x,y;
x=15;
y=13;
if(x > y){
cout<<“x is greater than y”; }
else{
cout<<“y is greater than x”;
return 0;}

23. Nested if…else Selection - Statement(general-form)
if (expression) {
if (expression1)
Statement-block1; }
else
Statement-block2;
Statement-block3;
If ‘expression’ is false the ‘statement- block3’ will be executed, otherwise it continues to perform the test for ‘expression 1’ . If the ‘expression 1’ is true the ‘statement block1’ is executed otherwise ‘statement-block2’ is executed

24. Else…if Selection
The expression is tested from the top (of the ladder) downwards. As soon as the true condition is found, the statement associated with it is executed.

25. Else…if Selection

26. Dangling - else Problem
The C++ compiler always associates an else with the immediately preceding if unless told to do otherwise by the placement of braces ({ and }). This behavior can lead to what’s referred to as the dangling-else problem.
(int x = 35; int y = 3; )

27. Dangling - else Problem

28. Blocks
The if selection statement expects only one statement in its body.
Similarly, the if and else parts of an if…else statement each expect only one body statement.
To include several statements in the body of an if or in either part of an if…else, enclose the statements in braces ({ and }). A set of statements contained within a pair of braces is called a compound statement or a block

29. Questions??