Question

What is role of void key in declaring function

Answer 1

Void functions are created and used just like value-returning functions except they do not return a value after the function executes. In lieu of a data type, void functions use the keyword "void." A void function performs a task, and then control returns back to the caller--but, it does not return a value. You may or may not use the return statement, as there is no return value. Even without the return statement, control will return to the caller automatically at the end of the function. A good utilization of a void function would be to print a header/footer to a screen or file. 

Remember: there are two kinds of subprograms that the C++ language utilizes: value-returning functions and void functions. Both value-returning functions and void functions receive values through their parameter lists. A value-returning function can only return one value to the calling environment. The caller invokes (calls) a value-returning function by using its name and argument list in an expression (i.e., 1. assignment, 2. output, or as an 3. argument in another function call):
In contrast, a void function (method or procedure, in other languages) does not return a function value. Nor is it called from within an expression. Instead, the function call appears as a complete, stand-alone statement. One example is the get function associated with the istream and ifstream classes.