Simple calculator in C V2
Other reviews already provided some pretty good points, so I'll just mention a few other things and reiterate on some already mentioned ones.


I would advise against function prototypes in this case. Since this is a single source file program, you could declare all functions before main() and avoid the prototypes. The problem with function prototypes is code duplication. If you change one function, at least two updates are mandatory, instead of just one. Avoid this extra maintenance overhead if you can.
For decimal division to work properly, you'll need a to use a floating-point type. My suggestion would be to use double instead of float. The float type is only recommended for storage and memory saving. Most CPUs operate natively on doubles and will convert a float to double when operating on a value. Since you don't have storage constraints, double is the best option.
Don't write noisy and obvious comments. The overall rule about code commenting is to use them to explain why you solved a problem in a given way, or to give any extra information (web links, mathematical formulas, etc) that will aid the understanding of a piece of code. Explaining what a code is doing should not be necessary if the code is well written. Well written code is self explanatory.
Arguably personal preference, but I find it better to properly space expressions and parameter list in function calls.


printf("\n%d + %d = %d\n",num1,num2,addition(num1,num2));



Better spacing:

printf("\n%d + %d = %d\n", num1, num2, addition(num1, num2));