If...
If
Syntax
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if logicalExpression statements end |
Examples
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% Generate a random number a = randi(100, 1); % If it is even, divide by 2 if rem(a, 2) == 0 disp('a is even') b = a/2; end |
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reply = input('Would you like to see an echo? (y/n): ','s'); if strcmp(reply,'y') disp(reply) end |
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x = 42; if exist('myfunction.m','file') && (myfunction(x) >= pi) disp('Expressions are true') end |
If/Else
Syntax
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if logicalExpression statements else catch-all statements end |
Examples
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% Generate a random number a = randi(100, 1); % If it is even, divide by 2 % Otherwise, multiply by 3 if rem(a, 2) == 0 disp('a is even') b = a/2 else disp('a is odd') b = a*3 end |
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reply = input('Do you like fruit? (y/n): ','s'); if strcmp(reply,'y') disp('Great, here is an apple') else disp('Ok, here is an orange') end |
If/ElseIf
Syntax
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if logicalExpression statements elseif alternative statements 1 elseif alternative statements 2 elseif alternative statements 3 end |
Examples
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% Generate a random number a = randi(100, 1); % If it is even and greater than 20, divide by 2 % If it is odd and less than 70, multiply by 3 if rem(a, 2) == 0 && a > 20 disp('a is even and greater than 20') b = a/2 elseif rem(a, 2) == 1 && a < 70 disp('a is odd and less than 70') b = a*3 end |
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reply = input('Choose a fruit? (a=apple, b=banana, o=orange): ','s'); if strcmp(reply,'a') disp('Great, here is an apple') elseif strcmp(reply,'b') disp('Banana...great choice!') elseif strcmp(reply,'o') disp('Ok, here is an orange') end |
If/ElseIf/Else
Syntax
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if logicalExpression statements elseif alternative statements else catch-all statements end |
Examples
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% Generate a random number a = randi(100, 1); % If it is even and greater than 20, divide by 2 % If it is odd and less than 70, multiply by 3 % Otherwise, set = 0 if rem(a, 2) == 0 && a > 20 disp('a is even and greater than 20') b = a/2 elseif rem(a, 2) == 1 && a < 70 disp('a is odd and less than 70') b = a*3 else disp('a is odd and greater than or equal to 70, or a is even and less then or equal to 20') b = 0 end |
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reply = input('Choose a fruit? (a=apple, b=banana, o=orange): ','s'); if strcmp(reply,'a') disp('Great, here is an apple') elseif strcmp(reply,'b') disp('Banana...great choice!') elseif strcmp(reply,'o') disp('Ok, here is an orange') else disp('You did not choose fruit from our list.') end |
Nested If
Unnecessary but Useful
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Necessary
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Variable Scope
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Break
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A = nan(20,1); for i=10:-1:-10 if(i <= 0) break; end A(i) = i; end A(:) |
Continue
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A = nan(20,1); for i=1:20 if(mod(i,2) == 0) continue; else A(i) = i; end end A |
Switch/Case Structure
Syntax
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switch switch_expression case case_expression statements case case_expression statements ... otherwise statements end |
Examples
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n = input('Enter a number: '); switch n case -1 disp('negative one') case 0 disp('zero') case 1 disp('positive one') otherwise disp('other value') end |
Switch/Case with Text
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Switch/Case Multiple Conditions
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Switch/Case Natural Break
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Switch/Case Examples
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x = [12 64 24]; plottype = input('What type of plot would you like? (pie, pie3, bar)'); switch plottype case 'bar' bar(x) title('Bar Graph') case {'pie','pie3'} pie3(x) title('Pie Chart') otherwise warning('Unexpected plot type. No plot created.') end |
Variable Scope
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Which to choose?
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Task Using If-Else
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Same Task Using Switch
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Switch Notes
The switch block tests each case until one of the case expressions is true. A case is true when:
For numbers, case_expression == switch_expression
For character vectors, strcmp(case_expression,switch_expression) == 1
An evaluated switch_expression must be a scalar or character vector.
The otherwise block is optional. MATLAB executes the statements only when no case is true.
When a case expression is true, MATLAB executes the corresponding statements and exits the switch block.
A case_expression cannot include relational operators such as < or > for comparison against the switch_expression. To test for inequality, use if, elseif, else statements.
If the first case statement is true, MATLAB does not execute the other case statements.
Do not use a break statement within a switch block. break is not defined outside a for or while loop.
Algorism and Bushism of the Day
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"In my sentences I go where no man has gone before." |
"Incredibly, while these 18 to 20 year-olds
cannot legally buy a beer, cannot purchase a bottle of wine and cannot order a drink
in a bar, right now they can walk into any gun shop, any pawn shop, any gun show,
anywhere in America and buy a handgun."
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Lesson of the Day
How do you know anything?
It isn't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.
Word of the day
SNAP