Pre-increment operator in C programming

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different answer in different compiler

in turbo c++ output is 21 and in any other output is 19.

C++

#include<stdio.h>
void main()
{
int i=4,x;
x= ++i + ++i + ++i;
printf("%d",x);
}

actual output is 19 how comes please explain it

What I have tried:

in turbo c++ output is 21 and in any other output is 19.

actual output is 19 how comes please explain it

Posted 17-Jun-19 7:02am

kumarsonu98520

Updated 17-Jun-19 10:05am

KarstenK

v2

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[no name] 17-Jun-19 13:04pm

Have a look here: Why does x = ++x + x++ give me the wrong answer?[^]

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Dave Kreskowiak · Answer 1 · 2019-06-17T07:24:00

Solution 1

The behavior of the pre- and post-fix operators in C are not exactly well-defined. The implementation of those operators varies from compiler to compiler.

Posted 17-Jun-19 7:24am

Dave Kreskowiak

Patrice T · Answer 2 · 2019-06-17T10:05:00

Quote:
actual output is 19 how comes please explain it

Simple, you are in the gray zone, the C compiler is free to rewrite your code the it sees fit.
Any formula with multiple increment/decrement on same variable in unpredictable, the result can also change with versions of same compiler or can depend on optimizations options.