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[Japo]

Yes, I wonder how you decided to put them. You need to review C syntax.

http://msdn.microsoft.com/en-us/library/66k51h7a.aspx

Also, why do you use system() so much? Instead of system("pause") you should use getchar() or similar, so the same thing is done by the program itself, instead of having to call an OS command. And what is the purpose of

system("TITLE Calculator");
system("COLOR 2");

? Are those actual executable files you have? Or are you trying to print those strings?

And you should import the header files with the prototypes for the functions you're using.