Why function prototype in c

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A prototype declares the function name, its parameters, and its return type to the rest of the program prior to the function's actual declaration. To understand why function prototypes are useful, enter the following code and run it:. This code compiles on many compilers without giving you a warning, even though add expects two parameters but receives only one. It works because many C compilers do not check for parameter matching either in type or count. You can waste an enormous amount of time debugging code in which you are simply passing one too many or too few parameters by mistake.

The above code compiles properly, but it produces the wrong answer. To solve this problem, C lets you place function prototypes at the beginning of actually, anywhere in a program. If you do so, C checks the types and counts of all parameter lists.

Try compiling the following:. Place one prototype for each function at the beginning of your program. They can save you a great deal of debugging time, and they also solve the problem you get when you compile with functions that you use before they are declared. Improve this answer. This is exactly the case where it's really simple to omit the prototype and just put the add function before main. Groo, I have edited the answer to include your comments as well.

Thank you. I prefer this way and never use prototypes in a single-file program. Prototypes should only be in header files in complex projects — phuclv. However, real programs not simple homework programs that are being used to teach a concept cannot be written the way you are envisioning. AND for gcc , the parameter: Wmissing-prototypes will cause the compiler to complain anytime any prototype is missing including this: int main. I just say that I prefer not use prototypes in very simple single-file programs, because it's useless and in that case there's not even a header file.

In big projects of course headers must be used, and still there should be no prototype in source file — phuclv. Show 1 more comment. But you can fix that by writing bar LL , or bar long long Or if the return type isn't int or void , then you also need the compiler to know about the function via a declaration. Peter Cordes Peter Cordes k 39 39 gold badges silver badges bronze badges. Add a comment. David Schwartz David Schwartz k 17 17 gold badges silver badges bronze badges. I think you are up to something here, but pls explain it more!!!!

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