C++ vs C# - array

Question

Let's have an array a = {0,1,2,3,4} and an int i = 2. Now let's do few operations in both (always starting from the point above).

a[i] = i++; // a = {0, 1, 2, 3, 4}
a[i] = ++i, // a = {0, 1, 3, 3, 4}

This seems logical to me. But for C++, I get different results:

a[i] = i++;  // a = {0, 1, 2, 2, 4}
a[i] = ++i;  // a = {0, 1, 2, 3, 4}

I don't understand the results I get in C++;

You can't really compare two very different languages with very different semantics like this. At least not without understanding the semantics in both languages very well, which would mean you would not actually need to ask this question. — Some programmer dude
– Some programmer dude, Commented Oct 2, 2017 at 11:14

Rakete1111 · Accepted Answer · 2017-10-02 11:21:57Z

7

C# evaluates from left to right, so in the first case, you get:

a[2] = 2; // 1)
a[2] = 3; // 2)

In C++, that is undefined behavior, but since C++17, an assignment operator is evaluated from right to left:

a[3] = 2; // 1)
a[3] = 3; // 2)

Different languages, different rules.

answered Oct 2, 2017 at 11:21

Rakete1111

49.5k19 gold badges133 silver badges173 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Thanks! That's what I was asking for :-)