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Asked: 2026-06-14T09:37:03+00:00

I’m learning C for 2 months. I experimented with different IDEs and my experiments

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I’m learning C for 2 months. I experimented with different IDEs and my experiments resulted in confusion. Because for e.g. in NETBEANS I can use abs function without stdlib.h library, but when I tried to do the same thing in Visual Studio 2012 it gave a an error. Or a very odd thing in NETBEANS I can use functions from math.h library without declaring the library. Why is this happening? Can someone help? NETBEANS USES cygwin compilers.

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  1. Editorial Team

    In C you don’t need to include the headers in order to use the functions. Older compilers don’t always warn about that though. Also, different compilers might provide those functions in different ways; on some, they’re not functions but macros. With macros, you need to include the headers.

    It’s good practice to always include the headers that provide the functions you need, so that you get the function prototypes. That’s the only way the compiler can check for errors (correct types of passed function arguments, for example.) If you call a function for which you have no prototype, you get an implicit declaration of that function. That means the compiler just takes a guess and hopes you’re using the function correctly, but has no way to check. That’s why this won’t work with macros, since a macro can’t have a function declaration (implicit or not.)

    The reason Visual Studio gives an error is because it’s a C++ compiler, not a C compiler. C++ is a bit different from C. One of the differences is that C++ does not allow implicit function declarations. If you don’t declare the functions you use (by including their header file in this case), then that’s considered an error. C++ is mostly compatible with C, but that happens to be one of the few differences.

    Btw, they’re not libraries. They’re header files. There’s a difference. You have several standard headers you can include, but you only have one library; the C library. On most systems, you also have a math library, which only contains math functions. The point though is that several header files can be (and usually are) part of the same library.

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