You missed the relevant text: >or equivalent; 10) >10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as char

You missed the relevant text: >or equivalent; 10) >10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as char * * argv, and so on. And Standard also says that: >or in some other implementation-defined manner. and: >In a freestanding environment (in which C program execution may take place without any benefit of an operating system), the name and type of the function called at program startup are implementation-defined. So main can be pretty much anything according to the Standard, depending on the system.