I have been trying to digest such references as Undefined behavior and sequence points and am interested as to why the outcome of the C++ variation of the following code is different from the outcome of a C# or Javascript variation of this code (see code samples, below).
Can you elaborate on this, what I think is an anomaly in this C-family variation? I appreciate it.
EDIT: This question is about a code example that would never exist in a real-world code base. The construct is undefined in C++, and why would you ever do such a thing? As @Sebastian says,
You have two pre-increments and one addition. C++ choses (in this case with your compiler, no guarantee) to combine the two pre-increments to +2 and then sum up 7+7. That is more performant. If you want to have a defined order, use more variables or put the operations into functions. You could write i = (i + 1) + (i + 2). That ist much easier to understand for humans, too!
EDIT: This appears then to be just a mind f**k for interviewees during a job interview. Best answer: "This is undefined."
C++ Code Example ( Link: https://g.nw7us.us/3nVy02j )
// CPP program to demonstrate special
// case of post increment operator
#include <iostream>
using namespace std;
int main()
{
int i = 5;
cout << "Value of i before pre-incrementing";
cout << "\ni = " << i;
i = ++i + ++i;
cout << "\nValue of i after pre-incrementing";
cout << "\ni = " << i;
cout << "\n+++++++++++++++++++++\n";
i = 5;
cout << "Value of i before pre-incrementing";
cout << "\ni = " << i;
i = ++i;
cout << "\ni = " << i;
i = i + ++i;
cout << "\ni = " << i;
return 0;
}
Output:
Value of i before pre-incrementing
i = 5
Value of i after pre-incrementing
i = 14
+++++++++++++++++++++
Value of i before pre-incrementing
i = 5
i = 6
i = 14
Now, here is the C# version ( link: https://g.nw7us.us/3nScCLz )
using System;
public class Program
{
public static void Main()
{
Console.WriteLine("Hello World");
int i = 5;
Console.WriteLine("i = [" + i + "]");
i = ++i + ++i;
Console.WriteLine("i = [" + i + "]");
}
}
Output:
Hello World
i = [5]
i = [13]
Finally, a Javascript example ( link: https://onecompiler.com/javascript/3xravf59k )
console.log("Preprocessing example...");
let i = 5;
console.log("i = [" + i + "]")
i = ++i + ++i;
console.log("i = [" + i + "]")
Output:
Preprocessing example...
i = [5]
i = [13]
I appreciate clarification on sequence points in C++, as it applies to this example.
