1. Conditional Logic
October 6, 2017

2. New vocab!!
Selection – A generic term for a type of programming statement that uses a Boolean condition to determine (i.e., select) whether or not to run a certain block of code.
This generally, but not always, refers to an if statement.
Know this for the AP!

3. Comparison Operators == “is equal to” != “is not equal to”
> “is (strictly) greater than”
< “is (strictly) less than”
>= “is greater than or equal to”
<= “is less than or equal to”
The AP exam will use > and <.

4. Comparison Operators (2 + 2) == 4 evaluates to TRUE.
"Joe Perry" == "joe perry" evaluates to FALSE (strings are case- sensitive).
"Ringo" <= "Ringo" evaluates to TRUE.
"TGOD" != "tgod" evaluates to TRUE.
N.B. Some languages will allow you to compare a string to a number (e.g., "3" == 3). C++ will give you an error if you try to do this!

5. Comparing Strings
Inequalities such as <= and >= can be used with strings—these perform a comparison in lexicographical order.
In English: which would come first in a dictionary?
Capital letters are "less than" lowercase letters since they have lower ASCII values.
"A" < "a"
"Dog" < "dog"
"dog" < "dogwood"

6. Logical Operators && AND || OR ! NOT
This is the character above \ (itself above Enter) on the keyboard.
! NOT

7. Logical Operators TRUE && TRUE evaluates to TRUE.
TRUE && FALSE evaluates to FALSE.
FALSE && TRUE evaluates to FALSE.
FALSE && FALSE evaluates to FALSE.

8. Logical Operators TRUE || TRUE evaluates to TRUE.
TRUE || FALSE evaluates to TRUE.
FALSE || TRUE evaluates to TRUE.
FALSE || FALSE evaluates to FALSE.

9. Logical Operators
!TRUE evaluates to FALSE.
!FALSE evaluates to TRUE.

10. Comparison Operators
N.B. Do NOT use a string of inequalities, such as the following:
if(x < z < y) {
cout << "z is between x and y.\n"; }
The proper way to do this is with the "and" operator:
if( (x < z) && (z < y) )

11. Logical Operators Consider the following code:
int cohen_age = 29;
cohen_age >= 21 && cohen_age < 30;
The bolded statement evaluates to TRUE.

12. Logical Operators Consider the following code:
int cohen_age = 29;
cohen_age >= 21 && cohen_age < 25;
The bolded statement evaluates to FALSE.
The following would evaluate to TRUE:
cohen_age >= 21 || cohen_age < 25;

13. Logical Operators Be careful with parentheses!
int cohen_age = 29;
string day = "Friday";
!((cohen_age == 29) && !(day == "Friday"))
The bolded code evaluates to TRUE.
cohen_age == 29 is TRUE.
day == "Friday" is TRUE—so !(day == "Friday") is FALSE.
TRUE && FALSE evaluates to FALSE.
!(FALSE) evaluates to TRUE.

14. Comparison Operators
Generally, comparison operators are used as part of if statements:
string band;
cout << "What is your favorite band?\n";
cin >> band;
if(band == "Aerosmith" || band == "aerosmith") {
cout << "Good answer.\n"; }
else
cout << "Try again.\n";

15. Comparison Operators
Generally, comparison operators are used as part of if statements:
int age;
cout << "What is your age?";
cin >> age;
if(age >= 21 && age <= 29) {
cout << "You're in the prime of your life.\n"; }
else
cout << "That's unfortunate.\n";

16. Logical Operators
OR has a slightly different meaning in logic than in ordinary usage.
Consider: “Is this elevator going up or down?”
We would normally answer “up” or “down.”
The logical answer is “yes”: either it is going up or it is going down.