How to search using wildcard in VIM

I think you're misunderstanding how the wildcard works. It does not match 0 or more characters, it matches 0 or more of the preceding atom, which in this case is y. So searching

/array*=

will match any of these:

arra=
array=
arrayyyyyyyy=

If you want to match 0 or more of any character, use the 'dot' atom, which will match any character other than a newline.

/array.*=

If you want something more robust, I would recommend:

/array\s*\[[^\]]\+\]\s*=

which is "array" followed by 0 or more whitespace, followed by anything contained in brackets, followed by 0 or more whitespace, followed by an "equals" sign.