A golf calculator? 29.

C:\test>perl -le"print eval while<>;"
2+2
4
3*5
15
$a=3**2+4
13
$a/2
6.5
(1+(2*3)+4)/($a%3)
11
^Z

C:\test>
[download]

Or with a Log₁₀ function: 53. (Note: capital L)

C:\test>perl -le"sub Log{log(pop)/log(10)}print eval while<>;"
Log(100)
2
10**2
100
Log(30)+log(40)
5.1660007088336
10**(Log(30)+Log(40))
1200
exp(log(30)+log(40))
1200
[download]

The -l is just used to add a newline to each print?

Why not use -p flag too, and have it do the reading and printing?

perl -lpe"$_=eval"
[download]

(works in a file, -e has issues under Windows)

Adding some error checking...

perl -ple'$_=eval||$@'

A calculator really should be able to tell you not to divide by 0, don't you agree? :-)

-sauoq
"My two cents aren't worth a dime.";

#!/usr/bin/perl -wnl
$_=eval();print;
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#!/usr/local/bin/perl -w
$|++; print "calc: ";
print eval, "\ncalc: "
while chomp( $_ = <STDIN> );
[download]

Pretty sure this code is simmilar to some other code I found round here somewhere, heh. It should do the job for you..

-- Can't never could do anything, so give me and inch, I'll make it a mile.

Here's hint though. Look at the eval() function.