Why the word "void" is always put infront of a function

As title, why the word "void" is used in front of a function ?

What is the function of this word ? and

why use "void" but other word ? thx

Read "Functions with no type. The use of void" in http://www.cplusplus.com/doc/tutorial/functions/.

joeydream:
As title, why the word "void" is used in front of a function ?

What is the function of this word ? and

why use "void" but other word ? thx

Functions can be written to return a value to the program that calls them. An example would be digitalRead(). The compiler needs to know and make allowances for that when the code is compiled and it also needs to know the type of data that will be returned. In order to do this the data type is put in front of the function name where it is defined.

However, many functions do not return data. An example would be digitalWrite(). In those cases the word void is used as the data type so that the compiler does not expect to return data.