-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathcontrol-structures.for.html
371 lines (364 loc) · 5.23 KB
/
control-structures.for.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
<HTML
><HEAD
><TITLE
>for</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.57"><LINK
REL="HOME"
TITLE="PHP Manual"
HREF="manual.html"><LINK
REL="UP"
TITLE="Control Structures"
HREF="control-structures.html"><LINK
REL="PREVIOUS"
TITLE="do..while"
HREF="control-structures.do.while.html"><LINK
REL="NEXT"
TITLE="foreach"
HREF="control-structures.foreach.html"><META
NAME="HTTP_EQUIV"
CONTENT="text/html; charset=ISO-8859-1"></HEAD
><BODY
CLASS="sect1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>PHP Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="control-structures.do.while.html"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 11. Control Structures</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="control-structures.foreach.html"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="control-structures.for"
><TT
CLASS="literal"
>for</TT
></A
></H1
><P
> <TT
CLASS="literal"
>for</TT
> loops are the most complex loops in PHP.
They behave like their C counterparts. The syntax of a
<TT
CLASS="literal"
>for</TT
> loop is:
<DIV
CLASS="informalexample"
><A
NAME="AEN3454"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> for (expr1; expr2; expr3) statement
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> The first expression (<TT
CLASS="replaceable"
><I
>expr1</I
></TT
>) is
evaluated (executed) once unconditionally at the beginning of the
loop.
</P
><P
> In the beginning of each iteration,
<TT
CLASS="replaceable"
><I
>expr2</I
></TT
> is evaluated. If it evaluates to
<TT
CLASS="literal"
>TRUE</TT
>, the loop continues and the nested
statement(s) are executed. If it evaluates to
<TT
CLASS="literal"
>FALSE</TT
>, the execution of the loop ends.
</P
><P
> At the end of each iteration, <TT
CLASS="replaceable"
><I
>expr3</I
></TT
> is
evaluated (executed).
</P
><P
> Each of the expressions can be empty.
<TT
CLASS="replaceable"
><I
>expr2</I
></TT
> being empty means the loop should
be run indefinitely (PHP implicitly considers it as
<TT
CLASS="literal"
>TRUE</TT
>, like C). This may not be as useless as
you might think, since often you'd want to end the loop using a
conditional <A
HREF="control-structures.break.html"
><TT
CLASS="literal"
>break</TT
></A
>
statement instead of using the <TT
CLASS="literal"
>for</TT
> truth
expression.
</P
><P
> Consider the following examples. All of them display numbers from
1 to 10:
<DIV
CLASS="informalexample"
><A
NAME="AEN3471"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> /* example 1 */
for ($i = 1; $i <= 10; $i++) {
print $i;
}
/* example 2 */
for ($i = 1;;$i++) {
if ($i > 10) {
break;
}
print $i;
}
/* example 3 */
$i = 1;
for (;;) {
if ($i > 10) {
break;
}
print $i;
$i++;
}
/* example 4 */
for ($i = 1; $i <= 10; print $i, $i++) ;
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> Of course, the first example appears to be the nicest one (or
perhaps the fourth), but you may find that being able to use empty
expressions in <TT
CLASS="literal"
>for</TT
> loops comes in handy in many
occasions.
</P
><P
> PHP also supports the alternate "colon syntax" for
<TT
CLASS="literal"
>for</TT
> loops.
<DIV
CLASS="informalexample"
><A
NAME="AEN3477"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> for (expr1; expr2; expr3): statement; ...; endfor;
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> Other languages have a <TT
CLASS="literal"
>foreach</TT
> statement to
traverse an array or hash. PHP 3 has no such construct; PHP 4 does
(see <A
HREF="control-structures.foreach.html"
>foreach</A
>). In PHP 3, you
can combine <A
HREF="control-structures.while.html"
>while</A
>
with the <A
HREF="function.list.html"
><B
CLASS="function"
>list()</B
></A
> and <A
HREF="function.each.html"
><B
CLASS="function"
>each()</B
></A
>
functions to achieve the same effect. See the documentation for
these functions for an example.
</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="control-structures.do.while.html"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="manual.html"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="control-structures.foreach.html"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><TT
CLASS="literal"
>do..while</TT
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="control-structures.html"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><TT
CLASS="literal"
>foreach</TT
></TD
></TR
></TABLE
></DIV
></BODY
></HTML
>