C + + Note 13: C + + extension--c++ all variables and functions must have a type

C + + all variables and functions must have a type;

C The default type in the language is not legal in C + +!

In C language can write some very strange function! and can run successfully!

What type is the return value of the F (i) function? What is the parameter type? We have a value of 10 to print out!

How many parameters can a G () function accept? We have no parameters, but we can add parameters when the function is called and run successfully!

F (i)

{

printf ("i=%d\n", I);

}

G ()

{

return 5;

}

int main ()

{

f (10);

printf ("G () =%d\n", G (1,2,3,4,5));

return 0;

}

Operation Result:

i = 10

G () = 5

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So this is the C language bad place, this bad place C + + has abandoned it!

The same code we put in C + + to see!

#include <iostream>

using namespace Std;

F (i)

{

printf ("i=%d\n", I);

}

G ()

{

return 5;

}

int main ()

{

f (10);

printf ("G () =%d\n", G (1,2,3,4,5));

System ("pause");

return 0;

}

Found compile error.

In C + +, whether it is a function return value type or variable type, or the number of function parameters, we can not be sloppy, C + + compiler will be able to find the error! The following program compiles before you can pass!

#include <iostream>

using namespace Std;

int f (int i)

{

printf ("i=%d\n", I);

return 0;

}

int g ()

{

return 5;

}

int main ()

{

f (10);

printf ("G () =%d\n", g ());

System ("pause");

return 0;

}

So C + + is more rigorous in the type checking of variables and functions!

Summary:

in C in Language

an int f () is a function that returns a value of type int and accepts arbitrary arguments;

an int f (void) represents an parameterless function that returns a value of type int.

in C + + in

int f () and int f (void) have the same meaning, all of which represent an parameterless function that returns a value of type int.

C + + emphasizes the type, and any program element must indicate the type.

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C + + Note 13: C + + extension--c++ all variables and functions must have a type