Ruby – 在一行上使用多个条件

if x > 100 && x % 2 == 1
    #Do something
end

但是,无论出于何种原因,这条线：

if (letters.eql? letters.upcase && dash.eql? '-' && numbers.to_i.to_s.eql? numbers)

惹错了很多错误.这与“.eql”有关吗？还是我还没有遇到过与Ruby无关的东西？

以下是其余代码供参考：

print "Enter license plate: ";
input = gets.strip;
if input.length == 8
    letters = input[0,2];
    dash = input[3];
    numbers = input[4,7];
    if (letters.eql? letters.upcase && dash.eql? '-' && numbers.to_i.to_s.eql? numbers)
        puts "#{input} is a valid license plate."
    else
        print "All valid license plates are three (3) uppercase letters,followed by a dash (-),followed by four (4) digits";
    end
else
    print "All valid license plates are 8 characters long.";
end

另外,这些是错误：

LicensePlate.rb:7: syntax error,unexpected tSTRING_BEG,expecting ')'
...? letters.upcase && dash.eql? '-' && numbers.to_i.to_s.eql? ...
...                               ^
LicensePlate.rb:7: syntax error,unexpected tIDENTIFIER,expecting ')'
... numbers.to_i.to_s.eql? numbers)
...