int a=5;cout<<++a + a++;//what is answer?

Question

This question seldom comes in Challenges. Answer of this question is 13.I have checked it on SoloLearn Code playground and on Code blocks. It comes same. But I don't know why every time when I type 13 while challenging it said Wrong??

Answer 1

The correct answer is : undefined behavior. That is: the result depends.
There is no rule in c++ that specifies the order of evaluation of operands of an operator. So i++ can be evaluated first this time and may be evaluated after ++i next time.
You may be confused: why 1+2-3 is evaluated from left to right?
The answer is: that's the associativity of operators, not the evaluation sequence.
This is one of the few subtle things one should be aware of when programming with c++.
Go to cppreference.com and look for Order of evaluation for more details. You will see the exact expression on the page. It is explicitly tagged as undefined behavior.

Answer 2

How it can be 12?when I saw this first time i agree with you i calculate it as 12.But why it comes 13 on software Tiago J Goncalves.

Answer 3

Code playground is wrong.
A is 5 -> no question
Cout << ++(increment a) a( give me the new value of a which is 6, now a is 6) + a(a is still 6) ++( increment a but the value is never printed because afyer you increment the code is not asking you to see the value) so tou have 12.
Try to cout<<a; after the code you have it will give you 13.

Answer 4

I have another question:
Cout<<++a + ++a; gives 14
Cout<<a++ + a++; gives 11
Why??

Answer 5

Ok i have the answer:
Cout<<a++; first prints out the original a and then adds 1 to it.
Cout<<++a; first adds 1 and then prints the result.

Answer 6

Code is read from left to right.
When you have ++a the code increments and gives you the value of a. When you have a++ the code gives the actual value of a and jncrements but doest show to you the value of a because you are not asking for it. If you want to see the values of a after ++a + a++ just add the following line: cout << a. And you will see 13. Read the code from left to right.

Answer 7

This Question which i asked and share,now has been removed from SoloLearn Challenges.

Answer 8

why not 13？

Answer 9

#include <iostream>
using namespace std;

int main() {
int a=5;
cout << ++a<<a++;
return 0;
}
Output is 75, does a++ have happens first than ++a?

Answer 10

++a + a++ for a=5: first we do ++a which means we add 1 To a before the opération so a become 6.then we add To 6 an other 6.so the result is 12.the opération a++ is done after the addition.so if we write cout<< ++a + a++ ;it gives 12 and cout<< a gives 7.

Answer 11

Output is 12

Answer 12

12

Answer 13

12