Use strpos, see here.

if (strpos($mystring, $findme) === false) {

    return false;
}

return true;

Be careful and use === false as the string position in the other string can be 0 which when using == will evaluate to false when it is actually true.

Use strpos

if (strpos($fistno, $secondno) !== false) {
    echo 'true';
}

You need to use == not just =

$check = 'this is a string 111';
if (strpos($mystring, $findme) === false) {
    echo 'perfect match';
} 
else {
    echo 'it did not match up';
}

= will assign the variable.
== will do a loose comparison.
=== will do a strict comparison.