Questions on Class and Function Calling

1. Let's look at the following:

#include <iostream.h>

class a {
private:
int x;
public:
a() {x=0;}
a(int z) {x=z;}
};

int main() {
a test1; // first command
a test2(3); // second command
a test3(); // third command
return (0);
}

I understand why the first and second command creates no error. But I dont understand why the third command always creates error? Is it normal? Do there exist any method to eliminate the problem? To me, the third command is virtually the same as the first command. But now the thrid creates the error but not the first one. So strange.

2. Let's look at the following:

#include <iostream.h>

void a() { // do something}

int main () {
a; // first command
a(); // second command
a(void); // third command
return (0);
}

Now, the first command creates error but not the second one. I want to know why. And what will happen to the third command?

Thanks for answering.

Quote:

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1. Let's look at the following:
...
Is it normal?

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Yes.

Quote:

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Do there exist any method to eliminate the problem?

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No, because it's not legal C++. Take another look at it. It looks alot like a function declaration doesn't it, which gives the compiler headaches.

Quote:

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2. Let's look at the following:
...
Now, the first command creates error but not the second one. I want to know why.

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because the second one calls the function , whereas the first is just the function name.

Quote:

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And what will happen to the third command?

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It'll fail to compile. void in this sense is used in declarations not in the calling of functions.

[quoteDo there exist any method to eliminate the problem?[/quote]

On second thoughts if you really want to use this syntax to call the default construct you can use new -


a* test3=new a();