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  exe-
       cution  of  body  are skipped; processing continues by invoking the Tcl
       interpreter on next, then evaluating test, and so on.  If a break  com-
       mand  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, vari-
       able substitutions will be made before the for command  starts  execut-
       ing,  which  means that variable changes made by the loop body will not
       be considered in the expression.  This is likely to result in an  infi-
       nite  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.  See below for an example:

EXAMPLES

       Print a line for each of the integers from 0 to 10:
              for {set x 0} {$x<10} {incr x} {
                 puts "x is $x"
              }

       Either loop infinitely or not at all because the expression being eval-
       uated  is actually the constant, or even generate an error!  The actual
       behaviour will depend on whether the variable x exists before  the  for
       command  is  run  and whether its value is a value that is less than or
       greater than/equal to ten, and this is because the expression  will  be
       substituted before the for command is executed.
              for {set x 0} $x<10 {incr x} {
                 puts "x is $x"
              }

       Print out the powers of two from 1 to 1024:
              for {set x 1} {$x<=1024} {set x [expr {$x * 2}]} {
                 puts "x is $x"
              }

SEE ALSO

       break, continue, foreach, while

KEYWORDS

       for, iteration, looping

Tcl                                                                     for(n)