Programming and Data Types

if, else, and elseif

if evaluates a logical expression and executes a group of statements based on the value of the expression. In its simplest form, its syntax is

if logical_expression
    statements
end

If the logical expression is true (1), MATLAB executes all the statements between the if and end lines. It resumes execution at the line following the end statement. If the condition is false (0), MATLAB skips all the statements between the if and end lines, and resumes execution at the line following the end statement.

For example,

if rem(a,2) == 0
    disp('a is even')
    b = a/2;
end

You can nest any number of if statements.

If the logical expression evaluates to a nonscalar value, all the elements of the argument must be nonzero. For example, assume X is a matrix. Then the statement

if X
    statements
end

is equivalent to

if all(X(:))
    statements
end

The else and elseif statements further conditionalize the if statement:

• The else statement has no logical condition. The statements associated with it execute if the preceding if (and possibly elseif condition) is false (0).
• The elseif statement has a logical condition that it evaluates if the preceding if (and possibly elseif condition) is false (0). The statements associated with it execute if its logical condition is true (1). You can have multiple elseifs within an if block.

if n < 0             % If n negative, display error message.
    disp('Input must be positive');
elseif rem(n,2) == 0 % If n positive and even, divide by 2.
    A = n/2;
else
    A = (n+1)/2;     % If n positive and odd, increment and divide.
end

if Statements and Empty Arrays

An if condition that reduces to an empty array represents a false condition. That is,

if A
   S1
else
   S0
end

will execute statement S0 when A is an empty array.

Flow Control

switch