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<H2><A NAME="SECTION00665000000000000000"> </A> <A NAME="2180"> </A><A NAME="2181"> </A>
<A NAME="conditional-statements"> </A>
<BR>
Conditional Statements, Branching
</H2>
<P>
As in FORTRAN 77 any of the following forms of the <TT>IF</TT> statement
may be used:<BLOCKQUOTE>
<TT>IF log_exp command </TT>! command = any MIDAS command<TT>
<BR>
</TT>! with at most 4 params.</BLOCKQUOTE>
<P></P>
<BLOCKQUOTE>
<TT>IF log_exp THEN </TT>! xyz = any logical expression<TT> <BR>
...
<BR>
ELSEIF log_exp THEN </TT>! uvw = any logical expression<TT> <BR>
...
<BR>
ELSE <BR>
...
<BR>
ENDIF</TT></BLOCKQUOTE>
<P></P>
<BLOCKQUOTE>
<TT>IF log_exp THEN <BR>
...
<BR>
ENDIF</TT></BLOCKQUOTE><TT>IF</TT> blocks may be nested up to 8 levels deep in a procedure.
<BR>
The logical expression <TT>`log_exp'</TT> is of the form:<BLOCKQUOTE>
<TT>arg1 op arg2</TT></BLOCKQUOTE>where <I>arg1, arg2</I> are either names of keywords (this includes also
the names P1, ..., P8) or constants, and <I>op</I> may be
any of <TT>.EQ.</TT>, <TT>.NE.</TT>,
<TT>.GT.</TT>, <TT>.GE.</TT>, <TT>.LT.</TT> or <TT>.LE.</TT> (with the same meaning as
in FORTRAN 77).
As with symbol substitution, specify single elements of an array and
substrings via,
e.g., <TT>OUTPUTI(7)</TT> and <TT>IN_B(2:15)</TT>.
<BR>
If we do<BLOCKQUOTE>
<TT>WRITE/KEYWORD INPUTC beer <BR>
WRITE/KEYWORD OUTPUTC wine <BR>
WRITE/KEYWORD INPUTR/R/1/3 1.,2.,3. </TT></BLOCKQUOTE>Then,<BLOCKQUOTE>
<TT>INPUTC .EQ. "beer" </TT>is TRUE<TT>
<BR>
INPUTC .EQ. "BEER" </TT>is also TRUE<TT>
<BR>
INPUTC .EQ. OUTPUTC </TT>is FALSE<TT>
<BR>
INPUTC(2:2) .EQ. OUTPUTC(4:4) </TT>is TRUE<TT>
<BR>
INPUTR(2) .GT. 5.4 </TT>is FALSE</BLOCKQUOTE>In string comparisons upper and lower case characters are not distinguished in
order to guarantee case insensitivity.
<BR>
Character keywords can only be compared to character keywords or character
constants (which are enclosed by double quotes). This can become tricky
in conjunction with symbol substitution:<BLOCKQUOTE>
<TT>!+ <BR>
! Example 13a, MIDAS procedure exa13a.prg <BR>
!+ <BR>
DEFINE/PARAM P1 ? N "Enter number: "
<BR>
DEFINE/MAXPAR 1 </TT>! only one parameter expected<TT>
<BR>
IF </TT><IMG
WIDTH="17" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img154.gif"
ALT="$\{$"><TT>P1</TT><IMG
WIDTH="16" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img155.gif"
ALT="$\}$"><TT> .EQ. 1 THEN <BR>
WRITE/OUT P1 = 1
<BR>
ELSE <BR>
WRITE/OUT P1 is not = 1
<BR>
ENDIF</TT></BLOCKQUOTE>Entering <TT>@@ exa13a 1</TT> as well as <TT>@@ exa13a 001</TT> will give the expected
output message <TT>P1 = 1</TT> since the line
<TT>IF </TT><IMG
WIDTH="17" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img156.gif"
ALT="$\{$"><TT>P1</TT><IMG
WIDTH="16" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img157.gif"
ALT="$\}$"><TT> .EQ. 1 THEN</TT>
has been converted in the first pass by the Monitor to
<BR>
<TT>IF 1 .EQ. 1 THEN</TT> or <TT>IF 001 .EQ. 1 THEN</TT> <BR>
and the two integer constants are equal. Now, consider the almost identical
procedure <TT>exa13b.prg</TT>:<BLOCKQUOTE>
<TT>!+ <BR>
! Example 13b, MIDAS procedure exa13b.prg <BR>
!+ <BR>
DEFINE/PARAM P1 ? N "Enter number: "
<BR>
DEFINE/MAXPAR 1 </TT>! only one parameter expected<TT>
<BR>
IF P1 .EQ. 1 THEN <BR>
WRITE/OUT P1 = 1
<BR>
ELSE <BR>
WRITE/OUT P1 is not = 1
<BR>
ENDIF </TT></BLOCKQUOTE>Entering <TT>@@ exa13b 1</TT> will return the error message
<TT>invalid IF statement...</TT> and abort. Why?
<BR>
Well, in the <TT>IF</TT> statement above the contents of the character keyword P1,
which is the character `1', is compared to the integer constant 1, an invalid
comparison.
<BR>
We modify the procedure once more:<BLOCKQUOTE>
<TT>!+ <BR>
! Example 13c, MIDAS procedure exa13c.prg <BR>
!+ <BR>
DEFINE/PARAM P1 ? N "Enter number: "
<BR>
DEFINE/MAXPAR 1 </TT>! only one parameter expected<TT>
<BR>
IF P1 .EQ. "1" THEN <BR>
WRITE/OUT P1 = 1
<BR>
ELSE <BR>
WRITE/OUT P1 is not = 1
<BR>
ENDIF</TT></BLOCKQUOTE>Now, entering <TT>@@ exa13c 1</TT> will work and yield
<TT>P1 = 1</TT> but <TT>@@ exa13c 001</TT> will output <TT>P1 is not = 1</TT> since the
string "001" is not equal to "1".
<BR>
<BR>
As another example let us see, how we can check if a parameter has been
entered at all:<BLOCKQUOTE>
<TT>!+ <BR>
! Example 14a, MIDAS procedure exa14a.prg <BR>
!+ <BR>
DEFINE/PARAM P6 + NUMBER "Enter first input number: " <BR>
IF P6(1:1) .EQ. "+" THEN <BR>
WRITE/KEYWORD INPUTC NONE </TT>! no P6 entered, set INPUTC accordingly<TT> <BR>
ELSE <BR>
WRITE/KEYWORD INPUTI/I/7/1 </TT><IMG
WIDTH="17" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img158.gif"
ALT="$\{$"><TT>P6</TT><IMG
WIDTH="16" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img159.gif"
ALT="$\}$">! store contents of P6 in INPUTI(7)<TT> <BR>
WRITE/KEYWORD INPUTC YES </TT>!indicate, that INPUTI holds a valid number<TT> <BR>
ENDIF</TT></BLOCKQUOTE>However, if we also want to check the limits of the given number we have to
use the <TT>DEFINE/PARAMETER</TT> command again, because testing "<TT>+</TT>"
against a numerical interval would lead to an error:<BLOCKQUOTE>
<TT>!+ <BR>
! Example 14b, MIDAS procedure exa14b.prg <BR>
!+ <BR>
DEFINE/PARAM P6 + NUMBER "Enter first input number: " <BR>
IF P6(1:1) .EQ. "+" THEN <BR>
WRITE/KEYWORD INPUTC NONE </TT>! no P6 entered, set INPUTC accordingly<TT> <BR>
ELSE <BR>
DEFINE/PARAM P6 + NUMBER "Enter first input number: " 22,1024
<BR>
WRITE/KEYWORD INPUTI/I/7/1 </TT><IMG
WIDTH="17" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img160.gif"
ALT="$\{$"><TT>P6</TT><IMG
WIDTH="16" HEIGHT="44" ALIGN="MIDDLE" BORDER="0"
SRC="img161.gif"
ALT="$\}$">! store contents of P6 in INPUTI(7)<TT> <BR>
WRITE/KEYWORD INPUTC YES </TT>!indicate, that INPUTI holds a valid number<TT> <BR>
ENDIF</TT></BLOCKQUOTE>Since, in the <TT>ELSE</TT> branch we know that parameter P6 is given, the default
value "<TT>+</TT>" itself is never tested against the interval [22,1024]. <BR>
<BR>
For testing multiple alternatives
use the <TT>BRANCH</TT> command. It has the syntax:
<BR>
<TT>BRANCH variable casea,caseb,...,casez labela,labelb,...,labelz</TT>.<BLOCKQUOTE>
<TT>!+ <BR>
! Example 15, MIDAS procedure exa15.prg <BR>
!+ <BR>
DEFINE/PARAMETER P1 ? C "Enter method: " <BR>
DEFINE/MAXPAR 1 </TT>! only one parameter expected<TT>
<BR>
! <BR>
! Use the first 2 characters of parameter P1 to distinguish the methods
BRANCH P1(1:2) AN,DI,HY ANALOG,DIGIT,HYBRID <BR>
! <BR>
! fall through if no match ... <BR>
WRITE/OUT Invalid option - please try again <BR>
RETURN
<BR>
! <BR>
ANALOG: <BR>
RUN ANALO <BR>
RETURN <BR>
! <BR>
DIGIT: <BR>
RUN DIGI <BR>
RETURN <BR>
! <BR>
HYBRID: <BR>
RUN HYBRI </TT></BLOCKQUOTE>Then, <TT>@@ exa15 ANALOG</TT> will execute the command <TT>RUN ANALO</TT> and
<TT>@@ exa15 digital</TT> or <TT>@@ exa15 di</TT> will run the program <TT>digi.exe</TT>.
<P>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-09</I>
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