Control Structures, If..else, switch..case

1. Algorithms and programming
basics
• Boolean operations
• Control structures
• if..else
• switch..case

2. Binary logic
• bool variable
• 1/0 – variable keep one of two variants
• It interpreter like true or false
• Binary logic is a statements, that gives one
result – true or false (0 or 1)
• 14>2 = 1(true)
• Example:
• int x = 12;
• x == 12
• Output: 1

3. Equality and relational operators
equality operator
or
relational operator
C++ equality
or rela tional
Operator
Example
of C++
condition
Meaning of
C++ condition
Relational operators
> > x > y x is greater than y
< < x < y x is less than y
 >= x >= y xis greater than or equal to y
 <= x <= y x is less than or equal to y
Equality operators
= == x == y x is equal to y
 != x != y x is not equal to y

4. Logical Operators
• Used as conditions in loops, if statements
• && (logical AND)
▫ true if both conditions are true
if ( gender == 1 && age >= 65 )
++seniorFemales;
• || (logical OR)
▫ true if either of condition is true
if ( semesterAverage>= 90|| finalExam >= 90 )
cout << "Student grade is A" << endl;

5. Logical Operators
• ! (logical NOT, logical negation)
▫ Returns true when its condition is false, & vice
versa
if ( !( grade == sentinelValue ) )
cout << "The next grade is " << grade << endl;
Alternative:
if ( grade != sentinelValue )
cout << "The next grade is " << grade << endl;

6. Control Structures
• Sequential execution
▫ Statements executed in order
• Transfer of control
▫ Next statement executed not next one in
sequence
• 3 control structures
▫ Sequence structure
 Programs executed sequentially by default
▫ Selection structures
 if, if/else, switch
▫ Repetition structures
 while, do/while, for

7. if Selection Structure
• Selection structure
▫ Choose among alternative courses of action
▫ Pseudocode example:
▫ If the condition is true
 Print statement executed, program continues to
next statement
▫ If the condition is false
 Print statement ignored, program continues
▫ Indenting makes programs easier to read
 C++ ignores whitespace characters (tabs, spaces,
etc.)

8. if Selection Structure
•if (logical statement)
•Action1;
•Else
•Action2;

9. if Selection Structure
• Translation into C++
If student’s grade is greater than or equal to 60
Print “Passed”
if ( grade >= 60 )
cout << "Passed";
• Diamond symbol (decision symbol)
▫ Indicates decision is to be made
▫ Contains an expression that can be true or false
 Test condition, follow path
• if structure
▫ Single-entry/single-exit

10. if/else structure
• “if” structure
▫ Make decision based on truth or falsity of
condition
▫ If condition met – body is executed, else - bodyis
not executed
▫ If there is an “else” structure
 Then if condition is false
the body of “else” structure
is executed

11. if/else structure
if(x > 10){
cout << "x is more than ten";
y = x * 2;
}
else
cout << "x is smaller";
• If there is more than one statements or expressions
in “if/else” structure use curly brackets { }

12. if/else Selection Structure
• if
▫ Performs action if condition true
• if/else
▫ Different actions if conditions true or false
• Pseudocode
if student’s grade is greater than or equal to 60
print “Passed”
else
print “Failed”
• C++ code
if ( grade >= 50 )
cout << "Passed";
else
cout << "Failed";

13. if/else Selection Structure
• Ternary conditional operator (?:)
▫ Three arguments (condition, value if true,
value if false)
• Code could be written:
cout << ( grade >= 60 ? “Passed” : “Failed” );
true
false
print “Failed” print “Passed”
grade >= 60
Condition Value if true Value if false

14. if/else Selection Structure
• Nested if/else structures
▫ One inside another, test for multiple cases
▫ Once condition met, other statements skipped
if student’s grade is greater than or equal to 90
Print “A”
else
if student’s grade is greater than or equal to 80
Print “B”
else
if student’s grade is greater than or equal to 70
Print “C”
else
if student’s grade is greater than or equal to 60
Print “D”
else
Print “F”

15. if/else Selection Structure

16. if/else Selection Structure
• if (logical statement){
• Action1;
• Action2;
• Action3;
• }
• Else
• Action4;
• if (logical statement){
• Action1;
• Action2;
• }
• Else{
• Action3;
• Action4;
• }

17. if/else Selection Structure
• Compound statement
▫ Set of statements within a pair of braces
if ( grade >= 50 )
cout << "Passed.n";
else {
cout << "Failed.n";
cout << "You must take this course again.n";
}
▫ Without braces,
cout << "You must take this course again.n";
always executed
• Block
▫ Set of statements within braces

18. Switch structure
• Used for testing variable for multiple values
• For each value the case keyword is used
• If no cases matched then optional default is used
• switch(){
▫ case value1: statements; break;
▫ case value2: statements; break;
▫ ……
▫ default: statements; break;
• }

19. Switch and nested if else
Switch structure is the same as nested if/else structure
that uses only equality comparison

20. Switch diagram

21. 52
Thanks for
your
attention!