为什么函数不能在 Main 之后

Question

Why can't I put a function after main, visual studio cannot build the program. Is this a C++ quirk or a Visual Studio quirk?

eg.

int main()
{
   myFunction()
}

myFunction(){}

will produce an error that main cannot use myFunction

Answer 1

You can, but you have to declare it beforehand:

void myFunction(); // declaration

int main()
{
   myFunction();
}

void myFunction(){} // definition

Note that a function needs a return type. If the function does not return anything, that type must be void .

Answer 2

You cannot use a name/symbol which is not yet declared . That is the whole reason.

It is like this:

i = 10;  //i not yet declared

int i;

That is wrong too, exactly for the same reason. The compiler doesn't know what i is – it doesn't really care what it will be.

Just like you write this (which also makes sense to you as well as the compiler):

int i;  //declaration (and definition too!)

i = 10;  //use

you've to write this:

void myFunction(); //declaration!

int main()
{
   myFunction() //use
}

void myFunction(){}  //definition

Hope that helps.

Answer 3

most of the computer programming languages have top to down approach which means code is compiled from the top. When we define a function after main function and use it in the main [myFunction () ], compiler thinks " what is this. I never saw this before " and it generates an error saying myFunction not declared. If you want to use in this way you should give a prototype for that function before you define main function. But some compilers accept without a prototype.

#include<stdio.h>
void myFunction(); //prototype
int main()
{
   myFunction(); //use 
}

myFunction(){ //definition 
.......;
}

Answer 4

Because

myFunction()

has to be declared before using it. This is c++ behaviour in general.

Answer 5

Functions need to be declared before they can be used:

void myFunction();

int main() {
  myFunction();
}

void myFunction() {
  ...
}

Answer 6

you have to forward declare a function so main can know that there is some.

void myFunction();

int main()
{
   myFunction();
}

void myFunction(){}

Don't forget about putting ; after each command.

Answer 7

在调用函数之前指定函数声明。这样编译器就会知道返回类型和签名

Answer 8

Declare then define.

void func();
int main()
{
    func();
}
void func()
{
}

Answer 9

You have to declare the function before.

void myFunction();

int main()
{
    myFunction()
 }

 myFunction(){}