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Re: st: single-line vs multiple-line -if- command
Hi,
Actually the explanation is in the help file:
http://www.stata.com/help.cgi?ifcmd
" Do not use the singe-line forms of if and else--do not omit the
braces--when the action includes the `++' or `--' macro-expansion
operators. For instance, do not code
if (...) somecommand `++i'
Code instead,
if (...) { somecommand `++i' }
In the first example, i will be incremented regardless of whether the
condition is true or false because macro expansion occurs before the
line is interpreted. In the second example, if the condition is false,
the line inside the braces will not be macro expanded and so i will not
be incremented.
The same applies to the else statement; do not code
else somecommand `++i'
Code instead,
else { somecommand `++i' } "
Tak Wai
Zurab Sajaia wrote:
Dear all,
I encountered a strange behavior -if- and/or macro inline incrementation
operators and was wandering what's going on.
Lets consider this example:
local a=1
local b=1
if 0 local a1=`a++'
if 0 {
local b1=`b++'
}
display `a', `b'
2 1
Although both expressions are false an therefore neither a1 nor b1 will
be created, `a' is incremented anyways. If we say that two versions of
-if- statement are equivalent then I'd expect exactly same outcome no
matter what type of commands and operations (like inline macro
substitution) is used. Am I confusing something here?
I would appreciate any thoughts about the issue,
Thanks,
Zurab
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