if statement

An if statement can appear anywhere a statement is expected. Its simplest form contains two key words if and end.
    if expression
       statement
    end
It is used to expression decisions. When the flow of program execution comes to an if statement, the expression is evaluated. If the logical value of the expression is true, statement will be executed. Otherwise, statement is skipped and the program moves to the point after end. For example
 x = rand(2);  // get two random numbers 

 // test if the point (x[1], x[2]) is inside the unit circle
 if norm(x) <= 1  
    in_circle = 1;
 end
If one wishes to execute certain commands when the expression is true, and some other commands when its false, a variant of the if statement that involves three keywords if, else, and end can be used.
    if expression
       statement group 1
    else
       statement group 2
    end
For example,
 if norm(x) <= 1  
    in_circle = 1;
 else
    in_circle = 0;
 end
If the first condition is tested to be false, further condition can be tested using the elseif keyword to determine if the second group of commands are to be executed. The following is the general form of an if statement.
    if expression 1
       statement group 1
    elseif expression 2
       statement group 2
    elseif expression 2
       statement group 2
    ...  // more elseif's
    else
       statement group n
    end

If expression 1 is true, then statement group 1 is executed. If expression 1 is false and expression 2 is true, then statement group 2 is executed. This goes on until the condition after one of the elseif's is true. If none of expression 1 to expression n-1 is true, statement group n is executed.

Note that each statement group can be one or several statements, and can also have nested control structures.

In the general form, the parts that start with elseif and else are optional.

oz 2009-12-22