raw/mann/for.n

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  10 '\" The definitions below are for supplemental macros used in Tcl/Tk
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 226 Command-Line Name:      \\fB\\$1\\fR
 227 Database Name:  \\fB\\$2\\fR
 228 Database Class: \\fB\\$3\\fR
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 246 .TH for n "" Tcl "Tcl Built-In Commands"
 247 .BS
 248 '\" Note:  do not modify the .SH NAME line immediately below!
 249 .SH NAME
 250 for \- ``For'' loop
 251 .SH SYNOPSIS
 252 \fBfor \fIstart test next body\fR
 253 .BE
 254
 255 .SH DESCRIPTION
 256 .PP
 257 \fBFor\fR is a looping command, similar in structure to the C
 258 \fBfor\fR statement.  The \fIstart\fR, \fInext\fR, and
 259 \fIbody\fR arguments must be Tcl command strings, and \fItest\fR
 260 is an expression string.
 261 The \fBfor\fR command first invokes the Tcl interpreter to
 262 execute \fIstart\fR.  Then it repeatedly evaluates \fItest\fR as
 263 an expression; if the result is non-zero it invokes the Tcl
 264 interpreter on \fIbody\fR, then invokes the Tcl interpreter on \fInext\fR,
 265 then repeats the loop.  The command terminates when \fItest\fR evaluates
 266 to 0.  If a \fBcontinue\fR command is invoked within \fIbody\fR then
 267 any remaining commands in the current execution of \fIbody\fR are skipped;
 268 processing continues by invoking the Tcl interpreter on \fInext\fR, then
 269 evaluating \fItest\fR, and so on.  If a \fBbreak\fR command is invoked
 270 within \fIbody\fR
 271 or \fInext\fR,
 272 then the \fBfor\fR command will
 273 return immediately.
 274 The operation of \fBbreak\fR and \fBcontinue\fR are similar to the
 275 corresponding statements in C.
 276 \fBFor\fR returns an empty string.
 277 .PP
 278 Note: \fItest\fR should almost always be enclosed in braces.  If not,
 279 variable substitutions will be made before the \fBfor\fR
 280 command starts executing, which means that variable changes
 281 made by the loop body will not be considered in the expression.
 282 This is likely to result in an infinite loop.  If \fItest\fR is
 283 enclosed in braces, variable substitutions are delayed until the
 284 expression is evaluated (before
 285 each loop iteration), so changes in the variables will be visible.
 286 For an example, try the following script with and without the braces
 287 around \fB$x<10\fR:
 288 .CS
 289 for {set x 0} {$x<10} {incr x} {
 290         puts "x is $x"
 291 }
 292 .CE
 293
 294 .SH "SEE ALSO"
 295 break, continue, foreach, while
 296
 297 .SH KEYWORDS
 298 for, iteration, looping