for(n) Tcl for(n)
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NAME
for - ``For'' loop
SYNOPSIS
for start test next body
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DESCRIPTION
For is a looping command, similar in structure to the C for
statement. The start, next, and body arguments must be Tcl
command strings, and test is an expression string. The for
command first invokes the Tcl interpreter to execute start.
Then it repeatedly evaluates test as an expression; if the
result is non-zero it invokes the Tcl interpreter on body,
then invokes the Tcl interpreter on next, then repeats the
loop. The command terminates when test evaluates to 0. If
a continue command is invoked within body then any remaining
commands in the current execution of body are skipped;
processing continues by invoking the Tcl interpreter on
next, then evaluating test, and so on. If a break command
is invoked within body or next, then the for command will
return immediately. The operation of break and continue are
similar to the corresponding statements in C. For returns
an empty string.
Note: test should almost always be enclosed in braces. If
not, variable substitutions will be made before the for
command starts executing, which means that variable changes
made by the loop body will not be considered in the
expression. This is likely to result in an infinite loop.
If test is enclosed in braces, variable substitutions are
delayed until the expression is evaluated (before each loop
iteration), so changes in the variables will be visible.
For an example, try the following script with and without
the braces around $x<10:
for {set x 0} {$x<10} {incr x} {
puts "x is $x"
}
KEYWORDS
for, iteration, looping
Page 1 (printed 2/19/99)
