Matvec Users’ Guide

Chapter 4
Program Flow Control
The program flow-control statements provided by Matvec are quite rich: if, while, for, break, continue, repeat,
and null. They are similar to those in the C/C++ language:
A BLOCK construction is defined as either a single statement or a sequence of statements (not necessary
to be in the same line) enclosed with braces. For instance
x = 8;
is a BLOCK, and
{
}
a = 6;
b = sample(3,5);
is a BLOCK, too.
4.1 If–Endif and If–Else Statements
The if statement has two forms:
if (expression) BLOCK1 endif
if (expression) BLOCK1 else BLOCK2
The expression must evaluate to a scalar, otherwise a run-time error will result.
In the first form of if statement, it simply performs a test on the expression in the parenthesis, and if
the expression evaluates to a non-zero scalar, the statement(s) in BLOCK will be executed. The endif is
mandatory to tell Matvec interpreter not to expect an else-branch.
In the second form of if statement, it performs a test on the expression in the parenthesis, and if the
expression is true then executes BLOCK1 otherwise execute BLOCK2.
A nested if is an if that is the part of a BLOCK belonging to another if or else. In Matvec an elsebranch
always refers to the nearest if statement that is within the same block as the else and is not already
associated with an if. For example,
if (i) {
if (j) BLOCK1 endif;
if (k) BLOCK2 else BLOCK3
}
else {
BLOCK4
}
35