def add_strings(num1, num2)

carry,result,num = 0,"",num

(0...(num1.size-num2.size)).each {num2 = '0'+num2 } if num1.size>num2.size

(0...(num2.size-num1.size)).each {num1 = '0'+num1 } if num2.size>num1.size

(1..num1.size).each do |i|

num = (num1[-i].to_i+num2[-i].to_i+carry)%10

carry = (num1[-i].to_i+num2[-i].to_i+carry)/10

result = num.to_s+result

end

result = '1'+result if(carry!=0)

return result

end