read number in if sentences

• Apr 30, 2007

• #2

prost

Structural

Jan 2, 2002

583

that syntax is wrong; Fortran generally doesn't use
two equal signs "==" for that purpose.

 

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• Apr 30, 2007

• Thread starter
• #3

albert1981

New member

Feb 16, 2007

61

prost,
if I put a number is working:

parameter=5

Read(1,*)a
If (a==(5))
read(1,*)b
write(2,*)b
end if


but not if I put:
If (a==(parameter))

 

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• May 1, 2007

• #4

johnhors

Aerospace

Jan 21, 2004

1,021

By default both parameter and a are real floating point numbers. It is considered bad fortran practice to compare two real numbers for equality, since you are relying too much on the precision of the hardware and software. Variable a may be stored as 5.0000001 and parameter may be stored as 4.99999999


Also 5 on its own is considered to be an integer, you should use 5.0 for single precision or 5.0D0 for double precision.

 

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• May 1, 2007

• #5

zeitghost

Computer

Oct 8, 2003

400

And in the dear dead days beyond recall "==" was .EQ.

 

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• May 1, 2007

• #6

johnhors

Aerospace

Jan 21, 2004

1,021

I still use .EQ. !

 

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• May 1, 2007

• Thread starter
• #7

albert1981

New member

Feb 16, 2007

61

johnhors,

It still doesn't work even If I define parameter and a as integer or as real.

 

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• May 1, 2007

• Thread starter
• #8

albert1981

New member

Feb 16, 2007

61

If I use:

If (a==(parameter))

it says "user breakpoint called from code 0x7c901230".

 

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• May 1, 2007

• #9

prost

Structural

Jan 2, 2002

583

what level of Fortran did they introduce "=="? I too still use .EQ.

 

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• May 1, 2007

• #10

xwb

Computer

Apr 29, 2005

535

Try using something else other than parameter. parameter is a keyword; not a reserved word: just a keyword. It is recognized as part of the syntax and you are allowed to use it but it can be confusing and some compilers may not like it.

In Fortran, if you don't declare a variable, and it begins with letters a-h, o-z, it is real. Real, real comparisons don't always work.

Code:

prorgram main
integer:: param, a, b
param = 5

read(1,*)a
if (a .eq. param) then
   read(1,*)b
   write(2,*)b
end if
stop
end

 

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• May 1, 2007

• Thread starter
• #11

albert1981

New member

Feb 16, 2007

61

Thanks to everybody now is working!

 

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• May 2, 2007

• #12

zeitghost

Computer

Oct 8, 2003

400

The relief is palpable...

.EQ. rules ok... )

 

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• May 3, 2007

• Thread starter
• #13

albert1981

New member

Feb 16, 2007

61

ehehehe thanks again

 

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• Jun 29, 2007

• #14

DanTex

Structural

May 25, 2001

84

I think you all will find that "==" is nowadays much more commonly used than ".EQ.". I'd venture that this has been true for more than 10 years now for those working with Fortran90 or beyond.

Also... the above code now works due to the use of the variable PARAM. The symbol used to check for equality is irrelevant.

Dan
dan@dtware.com

 

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• Jul 3, 2007

• #15

zeitghost

Computer

Oct 8, 2003

400

Never.

The sky is falling...

"==" in FORTRAN.

Doomed, I tell ye, doomed.

 

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