How can i call class constructor .

Question

I can't call class constructor i don't know why but when i define class in the main function . it must be call constructor automatically but it does not work . .
https://code.sololearn.com/caqich0G74A8/?ref=app

Answer 1

write without brackets. A a;

Answer 2

You're missing a semi-colon at the end of class declaration.
And you don't need parenthesis on object.

A a; //not A a();

Answer 3

Akib Reza nillyhan i added something . please look at again . and when i write A a an error occurs.

Answer 4

try to do it in second constructor.

A(int a=5) : k(a) {}

and call it from main like,

A a(5); or A a(6);

Answer 5

nillyhan i did it and the second constructor worked . but first one didn't. i wanted the first one to work .

Answer 6

first one is default constructor. you must not put any parameter inside it's parenthesis. write it as A() : k(5) {}.

Now calling " A a; " from main() would put 5 into k by default.

Answer 7

nillyhan i did everything as you said . but an error occurred again.

Answer 8

nillyhan please look at my code again.

Answer 9

A a() is a function declaration, a function called a, returning an object A and taking no arguments.
It's not a variable definition.

A a() is also called a vexing parse, because this is not what you would expect to happen and a common beginner mistake.

A a; would make it a variable without arguments.

Now A has to call a suitable constructor.

A has 2 constructors:
1. A(), a constructor taking 0 arguments
2. A(int a=5), a constructor taking 0 or 1 argument

Which one should it call?
A() or A(int a=5)?

It doesn't know either, this is an ambiguity error and causes the program to be rejected.

So either remove the default constructor or the default parameter to fix that.

Answer 10

oh I missed it earlier, sorry. edit the second constructor. remove "=" and write it like

A(int a) : k(a) {}

Answer 11

yes, as Dennis said

Answer 12

Dennis oh i got it thanks . the compiler does not know which one has to call.

Answer 13

nillyhan thanks a lot