Compiler not working? Hangs on execute.

[RungeKutta4]

Working in Windows 7. Using mingw (but also vs2015 is not working). Previously compiled programs execute as expected. Newly compiled programs do not report an error, but newly created a.exe hangs on execution. I am unable to end the process using Windows Task Manager (it always appears in triplicate), so I cannot delete the a.exe to retry. I have to restart my computer. What could I have messed up? Thanks!

[coder777]

When your program is executing the compiler work is done. Hence it is (certainly) a problem in your program. Probably some undefined behavior.