Why do we need prototype declaration

Check out our Data Structures in C course to start learning today. Next Static functions in C. Recommended Articles. Can we access private data members of a class without using a member or a friend function? How to print range of basic data types without any library function and constant in C? Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? The scope of the function prototype in C is determined by its position in the program. Generally, the function prototype is placed after the header file in the program.

The scope of the function prototype is considered within the same block as the function call. For example, the standard math library function sqrt has a double type parameter in the function prototype. However, it can be called with an integer argument and works perfectly. As we talked earlier about conversion feature, the compiler converts a copy of integer value 16 to the double Note: Please follow C programming usual arithmetic conversion rule to avoid truncation error.

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. For example, the following code will not compile:.

Why, you might ask, will it compile when add returns an int but not when it returns a float? Because older C compilers default to an int return value.

Using a prototype will solve this problem. Old style compilers do no error checking on parameter lists. Sign up for our Newsletter! Mobile Newsletter banner close.