How to make code executable depends on what language you're using. There are two main types of executable code: that which is executed directly by the CPU, and that which is interpreted by another program. C falls into the first, Perl into the second, and Java is a hybrid (the code is compiled into Java byte codes, but those byte codes are interpreted by the JVM). BASIC also falls into the second, although there are compileable BASICs out there, just to muddy the waters.

To run a C program on a computer (Linux, Windows or any other OS) you will need a C compiler. This will usually come with the other tools you need, which are a preprocessor, linker and there could be others depending on the installation. Compilers also often come with the SDK - software development kit, which contains header files and libraries suitable to the environment you're working in.

So to avoid typing in a huge if/else tree, what language do you want to use, and what OS do you prefer?

A quick google finds http://www.thefreecountry.com/compilers/basic.shtml
Since you repeat "easy" over and over, I would strongly recommend using some kind of BASIC. With BASIC you can just type the program into the IDE (integrated development environment) and run it straight away, without all that messing around with compiling and the rest of it. The appropriate language depends on what you want to do with it; if you want to look into becoming a professional programmer at some point in the future then you absolutely must know C. OTOH, if it's just hobby messing around, BASIC will probably cover 99% of your needs.