How is this right?

Question

So I started learning C++, after the basics I got a quiz.

It had a code:

{
int a=3;
int b=2;
b=a++;
cout<<++b;
}

The right answear was 4.
I don’t understand how.
C++ shell told me: “cout was not declared in this scope”
Basically it wasn’t right.

Can you please explain it to me?

Answer 1

If the C++ told you that cout was not declared in this scope, it was because the code snippet you posted did not include the header <iostream>. This header is used for input and output, and without it; it will not recognize cout as a function.

The answer was 4 because a = 3, and b = 3. Then b was reassigned to equal a++. So, b= a++. This means b = a = a + 1 (I know, it's weird). Then, it is printed as ++b, and this means 1 + b = b. It is assigned the value 4, before being printed. So, it prints 4.

I hope I helped at least a little. 😂 It is kinda hard to describe.

Answer 2

first assign values for a and b.
then reassign b value to be a++, which means increase a value by one (3+1=4) then assign it to b.
cout<<++b; means type on the screen the actual value of b (which is 4); then increase its value by one (4+1=5).
if you want to be more sure add a new line: cout<<b; (👈this will type 5 on the screen now).

Answer 3

Well yea, you could help me now I understand what kind of mistake I did. Thank you sir

Answer 4

You can check out the comment section in the quiz. There are quite a number of answers.

Basically, a++ is a post-increment operator (executed after the statement) while ++b is a pre-increment operator (executed before the statement). For more information, read these:
http://www.tutorialspoint.com/cplusplus/cpp_increment_decrement_operators.htm
http://en.cppreference.com/w/cpp/language/operator_incdec

Here is the equivalent code in case you don't understand the explanatons:

#include <iostream>

uisng namespace std;

int main()
{
int a = 3;
int b = 2;

// replace b=a++;
b=a;
a+=1;

// replace cout<<++b;
b+=1;
cout<<b;

return 0;
}