salesforce apex - string must be 6 digits and numeric only

in this apex code the expected output was not getting the question is Take a string type of variable

string pincode = '500038';

• Pincode must be exactly 6 digits, if the number of digits not equal to 6 then print "Pincode must be 6 digits"
• Pincode must be numerics only, if user enters alphabets then show error message "Pincode must be numerics only"

I tried this code

    string pincode = '500038';
    if (pincode.isNumeric()) {
     system.debug('Pincode must be numeric only');
       if (pincode.len == 6) {
    system.debug('Pincode must be 6 digits');
}

}