@sridhar2rok: I just entered the absolute path to my C program in the Command field, e.g.:
C:/Users/JDoe/SomeFolder/CompiledCProgram.exe
But getting the program to execute was only a fraction of the challenge for me. Most of my time was spent figuring out how to get the input data in just the right format for the program. That took a bit of experimenting and a lot of staring at debugger node outputs
Note that I said you have to use the full path to the command, not ./command.
Also if you need to use sudo then you will have to tell the system that the node-red user does not need to enter a password to run that command with sudo. Better is to make sure that the node-red user has access to whatever the command needs to access, so you don't need to use sudo.