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<TITLE>AN EXAMPLE</TITLE>
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<A NAME="lbAI"> </A> <H2>AN EXAMPLE</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>
<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,<A HREF="http://localhost/cgi-bin/man/man2html?5+SCORE">SCORE</A>(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>
<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>
<PRE>
$ ftnchek <A HREF="list.html">-list</A> <A HREF="symtab.html">-symtab</A> average
FTNCHEK Version 3.3 November 2004
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,<A HREF="http://localhost/cgi-bin/man/man2html?5+SCORE">SCORE</A>(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 SUM/COUNT converted to
real
17 END
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 in module COMPAV: Variables declared but never referenced:
J declared at line 11
Warning in module COMPAV: Variables may be used before set:
SUM used at line 14
SUM set at line 14
Statement labels defined:
Label Line StmtType
<30> 15 exec
18
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 in module AVENUM: Variables set but never used:
AVG set at line 43
I/O Operations:
Unit ID Unit No. Access Form Operation Line
5 SEQ FMTD READ 40
Statement labels defined:
Label Line StmtType Label Line StmtType
<80> 42 exec <100> 43 exec
0 syntax errors detected in file average.f
6 warnings issued in file average.f
Warning: Subprogram COMPAV argument data type mismatch at position 1:
Dummy arg SCORE in module COMPAV line 10 file average.f is type intg
Actual arg NUMS in module AVENUM line 43 file average.f is type real
</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:
<DL COMPACT>
<DT>1.<DD>
SUM and COUNT
should have been converted to real before doing the division.
<DT>2.<DD>
SUM should have been initialized to 0 before entering the loop.
<DT>3.<DD>
AVG was never printed out after being calculated.
<DT>4.<DD>
NUMS should have been declared INTEGER
instead of REAL.
</DL>
<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>
<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,<A HREF="http://localhost/cgi-bin/man/man2html?5+SCORE">SCORE</A>(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="lbAJ.html">INTERPRETING THE OUTPUT</A>
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