If Statements

1. If Statements • If statements: allow the computer to make a decision • Syntax: if (some condition) { then do this; } else { then do that; } no semicolons on the If or Else lines!

2. Comparing variables • When comparing variables (except Strings), use the double-equals ( = = ), NOT the equals sign! example: if (GPA = = 3.2)… • “Does not equals:” ! = • Greater than > • Greater than or equal to >= • Less than < • Less than or equal to <=

3. If-else if • If there are more than 2 possibilities, you must use the “else if” • Your final possibility should be the only “else” • Syntax: if (condition_1) { Statement_1; } else if (condition_2) { Statement_2; } else { Statement_3; }

4. And vs. Or • “and”  && (Statements will execute only if both conditions are true) • “or”  | | (Statements will execute if one condition is true) if ( score >= 80 && score < 90 ) { grade = ‘B’; }

5. A common mistake: If (score >= 80 && < 90) • You must put a variable before each <,>,==, <=, >=, etc….. • So the correct code would be: if (score >= 80 && score < 90)

6. When an and statement is false… • Very important: when && is used, once the compiler finds a part of the condition that is false, it ignores the rest of the condition, as well as whatever is inside the attached if-statement. • Example: int x = 0; int y = 0; if (x = = 1 && y = = 0) { System.out.println(“Hi”); } • In this example, once the compiler sees that x does not equal 1, it ignores everything that follows the &&, including y = = 0. • If this had been an || instead of a &&, then the condition would be true, and the if-statement would execute (“Hi” would be displayed).

7. When comparing Strings in an if statement, you DO NOT use = = • Instead, you must use .equals(“ “) or .equalsIgnoreCase(“ “) String dog = “Fido”; if (dog.equalsIgnoreCase(“fido”)) // true if (dog.equals(“fido”)) // false ***to use “does not equal” with a String: if (!(dog.equalsIgnoreCase(“penny”)))

8. Demo: IfDemo

9. Assignments • (Walter) Prompt the user to enter his or her first name, then (separately) their last name. • If the first OR last name is Walter, give all praise to the user. • If the first name is Walter and the last name is White, display “Heisenberg.” • **Only one of the above results should display, not both.** 2. (Numbahz) Prompt the user to enter a test score between 0 and 100. • Display what letter grade the score corresponds to. • Display whether the score is even or odd. • Display whether or not the score is divisible by 7. • If the score is 97, display “Yay” • If the score is not between 0 and 100, display “error”