What is user defined function and inbuilt functions in C?

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What is user defined function and inbuilt functions in C?
When you install a C compiler for a chip/operating system, there are going to be a bunch of inbuilt (or more commonly called built-in or system functions). The will be described (but not defined) in header files. Search the compiler folder and subfolders for *.h and you will see a lot of them. Open math.h (in read-only mode please) an you can scroll down and see some like sin(), cos(), tan().





User defined functions are functions that you create. For example:


----


#include %26lt;stdio.h%26gt;





void main()


{


printf("%d\n",add(3));


}





int add(int i, int j)


{


return i+j;


}


----


In this case add() is a user defined function. While printf() is a built-in function. You wrote add() but you did not write printf()





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