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diff --git a/tcl8.6/doc/for.n b/tcl8.6/doc/for.n new file mode 100644 index 0000000..9a3235f --- /dev/null +++ b/tcl8.6/doc/for.n @@ -0,0 +1,87 @@ +'\" +'\" Copyright (c) 1993 The Regents of the University of California. +'\" Copyright (c) 1994-1997 Sun Microsystems, Inc. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +.TH for n "" Tcl "Tcl Built-In Commands" +.so man.macros +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +for \- 'For' loop +.SH SYNOPSIS +\fBfor \fIstart test next body\fR +.BE + +.SH DESCRIPTION +.PP +\fBFor\fR is a looping command, similar in structure to the C +\fBfor\fR statement. The \fIstart\fR, \fInext\fR, and +\fIbody\fR arguments must be Tcl command strings, and \fItest\fR +is an expression string. +The \fBfor\fR command first invokes the Tcl interpreter to +execute \fIstart\fR. Then it repeatedly evaluates \fItest\fR as +an expression; if the result is non-zero it invokes the Tcl +interpreter on \fIbody\fR, then invokes the Tcl interpreter on \fInext\fR, +then repeats the loop. The command terminates when \fItest\fR evaluates +to 0. If a \fBcontinue\fR command is invoked within \fIbody\fR then +any remaining commands in the current execution of \fIbody\fR are skipped; +processing continues by invoking the Tcl interpreter on \fInext\fR, then +evaluating \fItest\fR, and so on. If a \fBbreak\fR command is invoked +within \fIbody\fR +or \fInext\fR, +then the \fBfor\fR command will +return immediately. +The operation of \fBbreak\fR and \fBcontinue\fR are similar to the +corresponding statements in C. +\fBFor\fR returns an empty string. +.PP +Note: \fItest\fR should almost always be enclosed in braces. If not, +variable substitutions will be made before the \fBfor\fR +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 \fItest\fR 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: +.SH EXAMPLES +.PP +Print a line for each of the integers from 0 to 9: +.PP +.CS +\fBfor\fR {set x 0} {$x<10} {incr x} { + puts "x is $x" +} +.CE +.PP +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 \fIx\fR exists +before the \fBfor\fR 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 \fBfor\fR command is +executed. +.PP +.CS +\fBfor\fR {set x 0} $x<10 {incr x} { + puts "x is $x" +} +.CE +.PP +Print out the powers of two from 1 to 1024: +.PP +.CS +\fBfor\fR {set x 1} {$x<=1024} {set x [expr {$x * 2}]} { + puts "x is $x" +} +.CE +.SH "SEE ALSO" +break(n), continue(n), foreach(n), while(n) +.SH KEYWORDS +boolean, for, iteration, loop +'\" Local Variables: +'\" mode: nroff +'\" End: |