while expression, statements,
end evaluates an expression,
and repeats the execution of a group of statements in a loop while
the expression is true. An expression is true when its result is nonempty
and contains only nonzero elements (logical or real numeric). Otherwise,
the expression is false.

Count the number of lines of code in the file magic.m. Skip blank lines and comments using a continue statement. continue skips the remaining instructions in the while loop and begins the next iteration.

fid = fopen('magic.m','r');
count = 0;
while ~feof(fid)
line = fgetl(fid);
if isempty(line) || strncmp(line,'%',1) || ~ischar(line)
continueend
count = count + 1;
end
count
fclose(fid);

An expression can include relational operators
(such as < or ==) and logical
operators (such as &&, ||,
or ~). Use the logical operators and and or to
create compound expressions. MATLAB^{®} evaluates compound expressions
from left to right, adhering to operator precedence rules.

Within the conditional expression of a while...end block,
logical operators & and | behave
as short-circuit operators. This behavior is the same as && and ||,
respectively. Since && and || consistently
short-circuit in conditional expressions and statements, it is good
practice to use && and || instead
of & and | within the expression.
For example,

x = 42;
while exist('myfunction.m','file') && (myfunction(x) >= pi)
disp('Expressions are true')
breakend

The first part of the expression evaluates to false. Therefore, MATLAB does
not need to evaluate the second part of the expression, which would
result in an undefined function error.

If you inadvertently create an infinite
loop (that is, a loop that never ends on its own), stop execution
of the loop by pressing Ctrl+C.

If the conditional expression evaluates to a matrix, MATLAB evaluates
the statements only if all elements in the matrix are true (nonzero).
To execute statements if any element is true, wrap the expression
in the any function.

To programmatically exit the loop, use a break statement. To skip the rest of
the instructions in the loop and begin the next iteration, use a continue statement.

When nesting a number of while statements,
each while statement requires an end keyword.