How to resolve “conflicting types error” in C?

Question

For the following C code (for swapping two numbers) I am getting the \"conflicting types\" error for swap function:

#include 
#includ         


        

Answer 1

You may wonder why the program compiles at all without a prototype for swap(), and that's because the compiler is more than a C99 tool. It also compiles C89 and K&R C programs.

C89 added the prototypes. Prior to C89, the compiler didn't need to see the declaration (the prototype) of a function unless it returned something other than int and the types of the formal parameters were not known to the compiler at all. The compiler just called every function with the types of the actual arguments, which received a set of default argument promotions to simplify things. The programmer would run the lint utility to cross-check actual and formal parameters. This program is still shipped with the BSD distributions.

K&R programs and their corresponding code styles are still accepted by your compiler, so when it sees a function for which no prototype is available it just goes ahead and calls it anyway.

In this case, you switch paradigms in between the call and the definition of the function. The K&R C assumptions the compiler made about the undeclared function when it had to generate a call turned out not to be valid. Even if you had written the whole program in the K&R style the compiler would have made the same complaints when it found out the real types of the function arguments.