Conditionals, part 2

1. Conditionals, part 2 switch statement “Nested” statements

2. 2. switch statement • Allows for evaluation of multiple cases of the sameparameter • The switch statement is looking for the parameter to have an exact matchto one of the cases. (No a<x && x<=b) • One case specification may have multiple values enclosed in braces( {…}). • The default case catches any values of the parameter other than the specified cases. • The default case should trap bad parameter values.

3. General Template switchparameter casespecification1 <code block> . . . casespecification n <code block n> otherwise <execute a default block> end There is no limit to the number of cases.

4. switch case: 1st Example • Let us review one of the previous example… switch month case {1,3,5,7,8,10,12} %31 days months days = 31; case 2 days = 29; %leap year to be coded.. case {4,5,9,11} %30 days months days = 30; otherwise disp(‘Invalid Entry.’) end Big advantage: reduces long OR statements of equality MUCH BETTER THAN ifmonth==1 || month== 3 || month== 5 || … month== 7 || month== 8 || month== 10 || month== 12 4

5. switch case: 2nd Example %ask user what he’d like to do menu_choice = input(‘Menu… (blablabla) 1 to 4: ’); %direct code to proper action switch menu_choice case 1 disp(‘You have selected 1.’) case {2,3,4} disp(‘You have selected a number from 2-4’) otherwise disp(‘Invalid Entry’) end

6. if versus. switch • As general ideas:

7. 3. Nested statements • “Nesting” means to encase one type of statement inside another. For example: Nested IF statements if length > 0 diameter = input('Diameter, please: '); if diameter > 0 volume = pi * (diameter / 2)^2 * length; end end Note that each if statement has its own end marker.

8. Nesting, cont. • The if, elseif, else, and end keywords each mark the beginning and end of the code under its control. • The elseif and else clauses of an if statement are optional. But you must include an end for every if statement – it marks the end of the code being executed conditionally. • It can be helpful to comment lines with end keywords so that it is clear which statement is being terminated: end % of switch

9. Nesting, cont. • Nesting can also mean using dissimilar statements – like nesting a switch within an if statement: if date > 20100101 %greater than January 1st 2010 switch month case {‘Dec’, ‘Jan’, ‘Feb’} disp(‘Winter’); case {‘Mar’, ‘Apr’, ‘May’} disp(‘Spring’); case {‘Jun’, ‘Jul’, ‘Aug’} disp(‘Summer’); case {‘Sep’, ‘Oct’, ‘Nov’} disp(‘Autumn’); end% of switch else disp(‘Date is too early’) end% of if date

10. Nesting, cont. • In fact, you can “nest” any MATLAB code you want inside of if statements, switch statements, or even… Loops!

11. Wrapping Up • switch statements only check EQUALITY • So you'll never ever see any relational operators (> < <= >=..) • If you do: you ARE definitely doing something wrong. • TRUST US. • They tremendously reduce if statements that check == with || statements. • The are very easy to use with numbers AND strings • We have not yet presented strings and if statements, since it is harder. • Nested if/switch are entirely feasible. Make sure the end keywords are correctly placed. Ctrl+A+I will remind you what MATLAB sees.