1. If Statements

2. Boolean Expressions Bools are a data type which take on two values:
1. true (1)
2. false (0)

3. Boolean Expressions
Bools can be used in a variety of expressions to express different logical statements.
a && b – true if both a and b are true
a || b – true if at least one of a and b are true
!a true if a is false
Other expressions produce bools:
a < b – true if a is less than b
a > b – true if a is greater than b
a <= b – true if a is less than or equal to b
a >= b – true if a is greater than or equal to b
a == b – true if a equals b
a != b – true if a does not equal b

4. Boolean Expressions
Try evaluating these expressions! In the following expressions a is true, b is false, c is 0, d is 1.
1. a && b
2. (b || b) && a
3. b || (b && a)
4. !a == b
5. !(b || (!a))
6. (a && b) || (c < d)
7. a + b
8. -2 < -1 < 1

5. Conditionals Sometimes we want to make choices.
If statements enable that!
int money = 10;
if (money < 5)
{cout << “lentils for dinner” << endl;}
else if (money < 10)
{cout << “burgers for dinner” << endl;}
else
{cout << “lobsters for dinner” << endl;}

6. Basic Syntax
if (condition) {
...
} else if (condition)
} else }

7. Sample Program #include <iostream> using namespace st
int main() {
double x = 0;
cout << “Please input a number: \n”;
cin >> x;
if (x < 0) {cout << “x is negative”;}
else if (x < 1) {cout << “x >= 0 and x <= 1”;}
else {cout << “x >= 1”;} }

8. Problems using if statements
1. Write an if statement that will print out “Yes” if at least one of the numbers a, b, and c are positive.
Base Code:
If (_____)
cout << “Yes”;
2. You are given an integer a. Write an if statement which will print out “fizz” if a is divisible by 3, “buzz” if a is divisible by 5 and “fizzbuzz” if a is divisible by both 3 and 5. (Hint: use % to check divisibility)

9. Gotchas
Assigning instead of testing for equality. What happens in the following statement?
int a = 0;
if (a = 1)
cout << “a equals 1”;
”a = 1” sets a to 1, and then returns the value of a. So it prints when it should not

10. Challenge Program
What does the following program output? What are the values of a and b after if statement?
int a = 0;
bool a = 0, b = 1;
if (a = b)
cout << “1: true\n”;
else
cout << “1: false\n”;
if (a = 0)
cout << “2: true\n”;
cout << “2: false\n”;
if (b = a)
cout << “3: true\n”;
cout << “3: false\n”;