for

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; 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.  See below for
       an example:

EXAMPLES
       Print a line for each of the integers from 0 to 9:

              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(n), continue(n), foreach(n), while(n)

KEYWORDS
       boolean, for, iteration, loop



Tcl                                                                     for(n)