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<HTML>
<HEAD>
<TITLE>an Example</TITLE>
</HEAD>
<BODY>
<A HREF="toc.html">Table of Contents</A><P>
<P>Previous: <A HREF="sect6.html">Using Project Files</A><HR><P>
<H2><A NAME="sect7" HREF="toc.html#toc7">an Example </A></H2>
The following simple Fortran program illustrates the messages
given by <B>ftnchek </B>. The program is intended to accept an array of test scores
and then compute the average for the series. <P>
<BR>
<PRE>
C AUTHORS: MIKE MYERS AND LUCIA SPAGNUOLO
C DATE: MAY 8, 1989
C Variables:
C SCORE -> an array of test scores
C SUM -> sum of the test scores
C COUNT -> counter of scores read in
C I -> loop counter
REAL FUNCTION COMPAV(SCORE,COUNT)
INTEGER SUM,COUNT,J,SCORE(5)
DO 30 I = 1,COUNT
SUM = SUM + SCORE(I)
30 CONTINUE
COMPAV = SUM/COUNT
END
PROGRAM AVENUM
C
C MAIN PROGRAM
C
C AUTHOR: LOIS BIGBIE
C DATE: MAY 15, 1990
C
C Variables:
C MAXNOS -> maximum number of input values
C NUMS -> an array of numbers
C COUNT -> exact number of input values
C AVG -> average returned by COMPAV
C I -> loop counter
C
PARAMETER(MAXNOS=5)
INTEGER I, COUNT
REAL NUMS(MAXNOS), AVG
COUNT = 0
DO 80 I = 1,MAXNOS
READ (5,*,END=100) NUMS(I)
COUNT = COUNT + 1
80 CONTINUE
100 AVG = COMPAV(NUMS, COUNT)
END
</PRE><P>
The compiler gives no error messages when this program is compiled. Yet
here is what happens when it is run: <P>
<BR>
<PRE>
$ run average
70
90
85
<EOF>
$
</PRE><P>
What happened? Why didn't the program do anything? The following is
the output from <B>ftnchek </B> when it is used to debug the above program: <P>
<P>
<BR>
<PRE>
$ ftnchek <A HREF="list.html">-list</A> <A HREF="symtab.html">-symtab</A> average
FTNCHEK Version 2.11 July 1999
File average.f:
1 C AUTHORS: MIKE MYERS AND LUCIA SPAGNUOLO
2 C DATE: MAY 8, 1989
3
4 C Variables:
5 C SCORE -> an array of test scores
6 C SUM -> sum of the test scores
7 C COUNT -> counter of scores read in
8 C I -> loop counter
9
10 REAL FUNCTION COMPAV(SCORE,COUNT)
11 INTEGER SUM,COUNT,J,SCORE(5)
12
13 DO 30 I = 1,COUNT
14 SUM = SUM + SCORE(I)
15 30 CONTINUE
16 COMPAV = SUM/COUNT
^
Warning near line 16 col 20: integer quotient expr converted to real
17 END
18
Module COMPAV: func: real
Variables:
Name Type Dims Name Type Dims Name Type Dims Name Type
Dims
COMPAV real COUNT intg I intg* J intg
SCORE intg 1 SUM intg
* Variable not declared. Type has been implicitly defined.
Warning: Variables declared but never referenced:
J
Warning: Variables may be used before set:
SUM
19
20 PROGRAM AVENUM
21 C
22 C MAIN PROGRAM
23 C
24 C AUTHOR: LOIS BIGBIE
25 C DATE: MAY 15, 1990
26 C
27 C Variables:
28 C MAXNOS -> maximum number of input values
29 C NUMS -> an array of numbers
30 C COUNT -> exact number of input values
31 C AVG -> average returned by COMPAV
32 C I -> loop counter
33 C
34
35 PARAMETER(MAXNOS=5)
36 INTEGER I, COUNT
37 REAL NUMS(MAXNOS), AVG
38 COUNT = 0
39 DO 80 I = 1,MAXNOS
40 READ (5,*,END=100) NUMS(I)
41 COUNT = COUNT + 1
42 80 CONTINUE
43 100 AVG = COMPAV(NUMS, COUNT)
44 END
Module AVENUM: prog
External subprograms referenced:
COMPAV: real*
Variables:
Name Type Dims Name Type Dims Name Type Dims Name Type
Dims
AVG real COUNT intg I intg MAXNOS intg*
NUMS real 1
* Variable not declared. Type has been implicitly defined.
Warning: Variables set but never used:
AVG
0 syntax errors detected in file average.f
6 warnings issued in file average.f
Subprogram COMPAV: argument data type mismatch
at position 1:
Dummy arg SCORE is type intg in module COMPAV line 10 file average.f
Actual arg NUMS is type real in module AVENUM line 43 file average.f
</PRE><P>
According to <B>ftnchek </B>, the program contains variables which may be used
before they are assigned an initial value, and variables which are not
needed. <B>ftnchek </B> also warns the user that an integer quotient has been
converted to a real. This may assist the user in catching an unintended
roundoff error. Since the <B><A HREF="symtab.html">-symtab</A> </B> flag was given, <B>ftnchek </B> prints out
a table containing identifiers from the local module and their corresponding
datatype and number of dimensions. Finally, <B>ftnchek </B> warns that the function
COMPAV is not used with the proper type of arguments. <P>
With <B>ftnchek </B>'s help,
we can debug the program. We can see that there were the following errors:
<OL>
<LI>SUM and COUNT should have been converted to real before doing the division.
</LI><LI>SUM should have been initialized to 0 before entering the loop. </LI><LI>AVG was
never printed out after being calculated. </LI><LI>NUMS should have been declared
INTEGER instead of REAL . </LI>
</OL>
<P>
We also see that I , not J , should have been
declared INTEGER in function COMPAV . Also, MAXNOS was not declared as
INTEGER , nor COMPAV as REAL , in program AVENUM . These are not errors,
but they may indicate carelessness. As it happened, the default type of
these variables coincided with the intended type. <P>
Here is the corrected
program, and its output when run: <P>
<BR>
<PRE>
C AUTHORS: MIKE MYERS AND LUCIA SPAGNUOLO
C DATE: MAY 8, 1989
C
C Variables:
C SCORE -> an array of test scores
C SUM -> sum of the test scores
C COUNT -> counter of scores read in
C I -> loop counter
C
REAL FUNCTION COMPAV(SCORE,COUNT)
INTEGER SUM,COUNT,I,SCORE(5)
C
SUM = 0
DO 30 I = 1,COUNT
SUM = SUM + SCORE(I)
30 CONTINUE
COMPAV = FLOAT(SUM)/FLOAT(COUNT)
END
C
C
PROGRAM AVENUM
C
C MAIN PROGRAM
C
C AUTHOR: LOIS BIGBIE
C DATE: MAY 15, 1990
C
C Variables:
C MAXNOS -> maximum number of input values
C NUMS -> an array of numbers
C COUNT -> exact number of input values
C AVG -> average returned by COMPAV
C I -> loop counter
C
C
INTEGER MAXNOS
PARAMETER(MAXNOS=5)
INTEGER I, NUMS(MAXNOS), COUNT
REAL AVG,COMPAV
COUNT = 0
DO 80 I = 1,MAXNOS
READ (5,*,END=100) NUMS(I)
COUNT = COUNT + 1
80 CONTINUE
100 AVG = COMPAV(NUMS, COUNT)
WRITE(6,*) 'AVERAGE =',AVG
END
$ run average
70
90
85
<EOF>
AVERAGE = 81.66666
$
</PRE><P>
With <B>ftnchek </B>'s help, our program is a success! <P>
<P><HR><P>Next: <A HREF="sect8.html">Interpreting the Output </A>
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