I'm compiling a program on my 64bit machine, but I'm not sure if it produces 32-bit or 64-bit output.. How can I check if a file is 32bit or 64bit on Windows?
You can use GNUfile for windows.
You can run the app thru PEID
Lastly (and preferred- less room for error)
With either Visual Studio C++ (at least express edition minimum) or the Platform SDK installed you can use dumpbin /headers to look at the PE header values.
The first value in the file header tells you the architecture: either 0x14C for x86 or 0x8664 for x64