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for(n)                                      Tcl Built-In Commands                                     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; pro-cessing processing
       cessing  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.  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 evaluated 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)