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Can anyone explain to me what this particular print statement does in a 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. an array that I didn't understand, cout <(i [ai]% N) [a + i-1] <"";

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1 answer


This is CBCPAT, a confusing but correct arithmetic trick.

Since subscribing to an array in C ++ (and C) is done using pointer arithmetic, if a

is an array and i

is an index (integer) then

a[i]

equivalent to

*(a + i)

and since addition is commutative, it is the same as

*(i + a)

which, in turn, can be written as

i[a]

I am. i.e. you are indexing an integer with an array (WTH?).

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



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

which is just

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

which in turn

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

i.e

*(a + i - 1 + 1)

which the

a[i]

Voila. Screw the programmer who wrote this shit.

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