CODEWITHSUNDEEP
c++arrays
sa_nyc
sa_nyc

Reputation: 981

Can anyone explain me what does this particular print statement do in for loop?

int a[] = { 1, 2, 3, 4, 5 };
const int N = sizeof(a)/sizeof(a[0]);
cout<<N<<endl;

for (int i = 0; i < N; ++i)
{
    cout << (i[a-i]%N)[a+i-1] << " ";
}

//It prints 1 2 3 4 5 i.e. the array what I didnt understand was cout << (i[a-i]%N)[a+i-1] << " ";

Upvotes: 3

Views: 208

Answers (1)

user529758
user529758

Reputation:

This is the CBCPAT, the Confusing But Correct Pointer Arithmetic Trick.

Since array subscription in C++ (and C) is done using pointer arithmetic, if a is an array and i is the index (an integer), then

a[i]

is equivalent to

*(a + i)

and since addition is commutative, this is the same as

*(i + a)

which in turn can be written as

i[a]

i. e. you're indexing the integer with the array (WTH?).

After having learnt this, you can easily rewrite the code to understand what it does: it is equivalent with

(a + i - 1)[(a - i)[i] % N]

which is just

(a + i - 1)[1 % N]

which is in turn

(a + i - 1)[1 % 5],

that is

*(a + i - 1 + 1)

which is

a[i]

Voilà. Screw the programmer who wrote this crap.

Upvotes: 15

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