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Question

#include<stdio.h>
int main()
{
int a = 2, b = 3;
a = a + b - (b = a);
printf("%d %d", a, b);
return 0;
}
Output: 3 2

Why output is 3 2??
According to priority, bracket should be solved first. Why (b = a) is not evaluated first? As it has brackets around it, increasing it's priority. So why it is not like this? >> a = a + b - (2) >> a = 2 + 2 - 2 (Cuz b is 2 now) >> a = 2. Why it is not like this? What's the meaning of bracket then? Priority should be given to brackets first? Please explain.

Answer 1

Angelo , A. S. , Jayakrishna🇮🇳 , Mr.Imperfect , Théophile and Ярослав Вернигора(Yaroslav Vernigora)

Thank you so much all of you. Now, I am clear about it. So grateful to have SoloLearn app! ✨😊

Answer 2

Hello First of all, I recommend you to learn "operator priority" This link will help you.
https://en.cppreference.com/w/cpp/language/operator_precedence

And here are the examples.
https://www.programiz.com/cpp-programming/operators-precedence-associativity

Answer 3

You are confusing execution with evaluation

a = a + b - (b=a)

First evaluates the components (in an undefined order):

a= 2 + 3 - (b=2)

Than it executes

(With parenthesis you change the order of execution)

Answer 4

As Angelo tried to say, we don't care about the result : it is UNDEFINED BEHAVIOR, meaning that nobody can predict the result.

As a general rule, we don't modify the value of a variable inside an expression, since it leads to undefined behaviors.

Answer 5

Maybe it's better with an example:

a= 2 * 3 + b

Evaluation:
a=2*3+3
Execution:
a=6+3
a=9

a=2*(3+b)

Evaluation:
a=2*(3+3)
Execution:
a=2*6
a=12

Answer 6

Hi! maybe it will help you to better understand the visualization of the code step by step. here on this site. true, I have never used it yet, and so I am not sure that it will work in your case, but still try it:

http://pythontutor.com

Answer 7

Evaluation expressions is left to right for equaliry operator.. here a = a + b -(b=a)
Here, before assigning b=a , first b is already gets replaced by its previous value 3. After that b value changed to a in stack so it is evaluated as a = 2+3-(2) = 3
So now a =3, b =2

but order of execution of expressions is compiler dependent in c/c++.

Answer 8

No, although there are some rules (that change between versions of c/c++), the order of evaluation is undefined

Answer 9

a=a+b-(b=a)
=> a=2+3-(b=2)
=> a=5-2
=> a=3
Than
print 3 2

Answer 10

According to first of all solve bracket then solve next
a=a+b-(b=a)
a=2+3-2
a=3
Then print
3 2
Because you are change value before print.

Answer 11

Angelo But why output is coming 3 2?

Answer 12

A. S. If 'b' becomes 2 then why first 'b' in the expression is taken as 3? Why not a=2+2-2 ??

Answer 13

C plus plus class I am new student