How to read an equation from a source file????

[nkcfjg]

i would like to read an equation of the type : (15**2-d**2)**0.5 with the variable d, with the command READ(7,*)C and it gives me an error message.Do i have to state that d is a variable???how???Any ideas?It is kind of urgent,because i have to deliver my homework at school...

 

[xwb]

You'll have to write a parser for that. You can't just read an expression in and expect the system to interpret it.

You could read in the value of d and get the program to compute the value though. Is that what's required?

 

[nkcfjg]

I thought there might have been a command to do that..Anyway the EQUATION must NOT be read from the source file, it must be read from e.g. input.txt .That means that if i want to calculate the value of d**10 instead of the equation above, i could simply do that by changing the equation in the file input.txt.I do not know what a parser is, but it doesn't sound like something that can easily be taught

 

[ArkM]

Fortran is a compiled language. There is no any compiler when your program runs. It's machine instructions compiled from your source code plus library modules. Executable code has no idea about

d

variable: it has machine word and its address - that's all.
The simplest expression parser in Fortran? Why not, but it contains more than 100 lines of code (some handreds, I think). But this parser don't know your code d variable too (see above)...

 

[nkcfjg]

Thanks anyway...Do you know any site that might have the parser i want??? Or something close to that, so that i can modify it?Are ther any sites with parsers? thanks for all the help. I appreciate that you answered to my question

 

[xwb]

I haven't seen any sites with parsers for arithmetic expressions in Fortran. Most of them are in C/C++, possibly using lex and yacc.

 

[ArkM]

You can see a simplest expression parser example in the excellent book "The C++ Programming Language" by Bjarne Stroustrup (calculator example). It's not so hard to rewrite it in modern (90/95, with recursion etc) Fortran (additionally you can see what Fortran borrowed from C++...

 

[xwb]

Have a look at

http://www.fortran.com/fortran/free.html

There are some parsers written in fortran but I don't know which compiler (77 or 95) they require.