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
|
<HTML>
<HEAD>
<TITLE>String variables</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF" TEXT="#000000">
<P><A NAME="variablestring"></A>
<font size="+2" color="green">String variables</font></P>
<P>
String variables can be used wherever strings are expected, such
as file names and keyword parameters.</P>
<P>
A string is defined to be a one dimensional array of ASCII
characters. A string can be a literal quote string, such as,
<code>'this is a quote string'</code>, or an expression that results
in a string, such as <code>RCHAR(35.6)</code>.</P>
<P>
A literal quote string may begin with the opening quote, <CODE>`</CODE> and
end with the single quote, <CODE>'</CODE>, or may begin
and end with the single quote, or may begin and end with the double quote,
<CODE>"</CODE>.</P>
<p>
<table>
<tr>
<td valign="top"><em><font color="red">Hint</font></em></a></td>
<td>The simplest way to include a single quote in a string is to use double
quotes to delimit the string, e.g., <CODE>"ABC'DEF"</CODE>. Similarly, to include
a double quote in a string, delimit the string with single quotes, e.g.,
<CODE>'ABC"DEF'</CODE>. Another method is to use the
<CODE><a href="../Functions/char.htm">CHAR</a></CODE>
function to convert the ASCII code for a quote into a character and append it to the
string using the <a href="../Operators/append.htm">append</a> operator,
<CODE>//</CODE>. For example: <CODE>'ABC'//CHAR(34)//'DEF'</CODE>,
since the ASCII code for <CODE>"</CODE> is <CODE>34</CODE>. The ASCII codes for
the standard characters can be found using the <CODE>
<a href="../Functions/ichar.htm">ICHAR</a></CODE> function.</td>
</tr></table></p>
<P>
A string variable is a single string, that is, a one
dimensional array of characters. A string array variable is an array of
strings. An element of a string variable is a single character.
An element of a string array variable is a string. There is no
maximum length for either a string variable or any element of a
string array variable, nor a maximum number of elements of a string
array variable. The elements of a string array variable need not be the
same length.</P>
<P>
The <a href="../Functions/clen.htm"><CODE>CLEN</CODE></a> function returns
a scalar value equal to the length of a string.</P>
<P>
A string variable, or an element of a string array variable, can be entered
directly by means of an assignment. For example:</P>
<P>
<font color="blue"><PRE>
TS='This is a string' ! string variable
TA[3]='This is a string' ! array string variable: third element
</PRE></font>
<P>
An entire string array variable can be created with the
<a href="../Commands/Read.htm"><CODE>READ/TEXT</CODE></a> command.</P>
<P>
Commands that expect strings, such as the
<a href="../Commands/Text.htm"><CODE>TEXT</CODE></a> command, which draws a string, or the
<a href="../Commands/Write.htm"><CODE>WRITE</CODE></a> command, which expects a file name
as a parameter, will only accept a single string. Remember, though,
that a string can be a literal quote string, a string variable,
<EM>one</EM> element of a string array variable, and/or some
combination of string functions and string operators.</P>
<P>
The following table shows all of the possible ways that a string
variable can be considered to be equivalent to a single string, that is,
can be used wherever a string is expected.</P>
<p>
Let <code>a</code> be a scalar and let <code>x</code> be a vector.
Suppose that <code>TA</code> is a string array variable and <code>T</code> is a string variable.</p>
<p>
<center>
<table cellpadding="2" cols="4">
<tr>
<td valign="top"><code>T</code></td><td valign="top">=</td>
<td valign="top"><code>T[i]</code></td>
<td valign="top">for <code>i = 1, ..., CLEN(T)</code></td>
</tr><tr>
<td valign="top"><code>TA[a]</code></td><td valign="top">=</td>
<td valign="top"><code>TA[a][i]</code></td>
<td valign="top">for <code>i = 1, ..., CLEN(TA[a])</code></td>
</tr><tr>
<td valign="top"><code>T[x]</code></td><td valign="top">=</td>
<td valign="top"><code>T[i]</code></td>
<td valign="top">for <code>i = x[1], x[2], ..., x[#]</code></td>
</tr><tr>
<td valign="top"><code>TA[a][x]</code></td><td valign="top">=</td>
<td valign="top"><code>TA[a][i]</code></td>
<td valign="top">for <code>i = x[1], x[2], ..., x[#]</code></td>
</table></center></P>
<P>
Strings may be appended together using the <a href="../Operators/append.htm">append</a> operator,
<CODE>//</CODE></a>. For example, suppose that <code>T</code> is a string variable with the value
<code>'this is a string'</code>. You can make a new string variable using the assignment:</P>
<P>
<code>T2='start of new string '//T//' end of new string'</code></P>
<P>
and <code>T2</code> will have the value:
<code>'start of new string this is a string end of new string'</code>.</P>
<P>
A variable name can be converted to a string by means of the
<a href="../Functions/varname.htm"><code>VARNAME</code></a> function. A
scalar <EM>value</EM> can be converted to a string by means of the
<a href="../Functions/rchar.htm"><code>RCHAR</code></a> function. For example,
if <CODE>A</CODE> is a scalar with the value <CODE>-1.234</CODE>, and <CODE>T</CODE> is a string
variable with the value <code>' units'</code>, then the assignment:</P>
<P>
<code>T2='The value of '//VARNAME(A)//' is '//RCHAR(A)//T</code></P>
<P>
makes a string variable <CODE>T2</CODE> with the value:
<code>'The value of A is -1.234 units'</code>.</P>
<P>
A format string is allowed as the second
argument of the <code>RCHAR</code> function. For example:</P>
<P>
<code>T2='The value of '//VARNAME(A)//' is '//RCHAR(A,'F4.1')//T</code></P>
<P>
makes a string variable <CODE>T2</CODE> with the value:
<code>'The value of A is -1.2 units'</code>.</P>
<P>
<a name="expression"></a>
<font size=+1 color="green">Expression variables</font></P>
<P>
String variables can be used in numeric expressions, as so called expression
variables, to shorten or to simplify an expression. Parentheses around an
expression variable are assumed during a numeric evaluation. For example:</P>
<P>
<font color="blue"><PRE>
T='A+B'
Y=X*T ! this is equivalent to Y=X*(A+B)
</PRE></font>
<P>
A string variable will be numerically evaluated if it is a numeric operand or
the argument of a numeric function. Otherwise, a string variable is treated as
a string. You can force numeric evaluation by using the
<a href="../Functions/eval.htm"><CODE>EVALUATE</CODE></a>
function. For example:</P>
<P>
<font color="blue"><PRE>
T='3+2' ! define T to be a string variable
=T ! the string '3+2' will be displayed
=EVALUATE(T) ! the numeric value 5 will be displayed
</PRE></font>
<P>
The <a href="../Functions/expand.htm"><CODE>EXPAND</CODE></a>
function produces a string by parsing the input string and expanding any expression
variables present in this string. If an expression variable, contained in
the original string, also contains expression variables, they are also
expanded, and so on until all such expression variables have been expanded.
Syntax checking is done during the expansion.</P>
<P>
The maximum length of a completely expanded expression is two thousand five
hundred (<CODE>2500</CODE>) characters.</P>
<P>
As an example of expression variable use, consider the following set of
instructions:</P>
<P>
<font color="blue"><PRE>
A=2 ! define a scalar A
B=3 ! define a scalar B
FC1='(A+B)/A' ! define a string variable FC1
FC2='SQRT(A/B)' ! define a string variable FC2
FC3='FC1*FC2' ! define a string variable FC3
FC4='FC3+4*FC2' ! define a string variable FC4
=FC4 ! displays 'FC3+4*FC2'
=EXPAND(FC4) ! displays '(((A+B)/A)*(SQRT(A/B)))+4*(SQRT(A/B))'
=EVALUATE(FC4) ! displays 5.3073
</PRE></font></P>
<P>
<a href="VariablesS04.htm"><img src="../shadow_left.gif">
<font size="+1" color="olive">Matrix variables</font></a><br />
<a href="VariablesS06.htm"><img src="../shadow_right.gif">
<font size="+1" color="olive">Making a vector</font></a>
</P>
</BODY>
</HTML>
|
