GetKeyUp() by array interaction issue.

Given the follow code snippet:

public string[] key;

void Update()
  for( int index = 0; index < key.Lenght; index++ )
    if( Input.GetKeyUp( key[index] ) )


At any key up time I ever get the exact index, i.e, any key into the range of array causes DoSomenthing() runs. But there is a interaction, why do array index matches to the exact key? Is it a correct use or is it a simply runtime mistake?

The method is called as many time as the value of the index. Very simple.