Why is i + ++i 12 when i is 5?

[coalzpp]

I was tried to add one more of i and i but the result was 12. The language I tried is c. Shouldn't it be 11?

#include <stdio.h>

int main() {

int i=5;

printf("%d", ++i + i);

}

i already tried the same thing in c++ and same result. How can the sum of a number plus one more of that number be equal to two more than twice that number?

 

[Deleted member 2829]

Your assumption is that i remains 5 and that ++i is the same as i+1. But that is not so !

i++

is a unary operator which increases i by one, then evaluates to the new value. So the first term evaluates to 6, and the second term as well, because i is now 6. Your code is equivalent to

i = i+1;
printf("%d", i + i);

I hope that clarifies. If not, you'll need to study C operators in more detail.
This would work the same way in C, C++, C# Java, and Javascript.

 

[coalzpp]

Your assumption is that i remains 5 and that ++i is the same as i+1. But that is not so !

i++

is a unary operator which increases i by one, then evaluates to the new value. So the first term evaluates to 6, and the second term as well, because i is now 6. Your code is equivalent to

i = i+1;
printf("%d", i + i);

I hope that clarifies. If not, you'll need to study C operators in more detail.
This would work the same way in C, C++, C# Java, and Javascript.

but when I replace ++i + i with i + ++i, it becomes 12. shouldn't it be 11?

 

[Deleted member 2829]

but when I replace ++i + i with i + ++i, it becomes 12. shouldn't it be 11?

I can see why you think so. But no, the ++ has higher precedence than the +, and is evaluated first. Remember that not everything is executed left to right ! You always need to be conscious of the order or operations. Whenever in doubt, use parentheses (although in this case it would not help). And personally I would never use + and ++ in the same expression. At least not in this manner. It's confusing and kind of defeats the purpose.

 

[Subba Rao]

according increment operator, we need to follow following rules (depends on compiler)
according to turbo c++
rule 1) check how many preincrements are available and assign the last incremented value through out the expression
rule 2) go for assignment operator
rule 3) check any post increments , if yes go for it

 

[Deleted member 2829]

Rule 1 is don't write cryptic code. There is no rule 2 😀