What is the main difference between returning value of a function and does not return any value of a function in  C. Which is correct void main(void), int main(void), int main(int) , or void main(int) and explain the main difference between int main() and int main(void). 

A function may or may not return a value to the calling function. If the function is returning a value, then you have to mention the data type in the function definition and funtion declaration (like int, float or double etc.). If the funtion not returning any value, then you have to mention the data type as void. If you not mention return type, then compiler take it as int data type.

 Similary, a function  may have arguments or not. If your functions have arguments, then you have to mention data types of arguments. If you are not passing any arguemtns then you may write void or simply live it blank that is depend upon the compiler. main() is a user defined function, so it follows the same rules.

Hi, Thanks for A2A, your 1st question is "What is the main difference between the returning value of a function and does not return any value of a function in  C". 

the main difference between both types of the function will be its return type as the function which will not return any value will have return type "void" which means nothing wherein function with the return value should have a return type "data type" int, char, struct so ....on..while declaring/defining both !! and one more major difference will be, function with no return type (or can say void return type ) don't need any additional variable to save its return value wherein function with return value may have addition variable or additional check for return value !! 

 now coming to your 2nd question "Which is the correct void main(void), int main(void), int main(int), or void main(int) and explain the main difference between int main() and int main(void)" 

ans: best practice is to use int main(void) if it does not have command line arguments !! now using void main(void) is fine but gives warning in some compilers as the main function expected to return integer value !! now int main(int) is incorrect !!