"条件字符串文字"是什么意思？

Question

每当我尝试运行程序时,会弹出一个错误,说"条件中的字符串文字(第10行)".我究竟做错了什么？

puts "Welcome to the best calculator there is. Would you like to (a) calculate the area of a geometric shape or (b) calculate the equation of a parabola? Please enter an 'a' or a 'b' to get started."
response = gets.chomp

if response == "a" or "A"

       puts "ok."

elsif response == "b" or "B"

       puts "awesome."

else

       puts "I'm sorry. I did not get that. Please try again."

end

Answer 1

你必须指定两侧的完整条件or.

if response == "a" or response == "A"

两边or没有连接; Ruby根据左边的内容不做任何关于右边的假设.如果右边是裸字符串"A",那么,除了false或被nil认为是"真" 之外的任何东西,所以整个表达式始终评估为"真".但Ruby注意到它是一个字符串而不是实际上是一个布尔值,怀疑你可能没有指定你的意思,因此在问题中发出警告.

您还可以使用case表达式使对单个值执行多个测试变得更简单; 如果您在单个中提供多种可能性的列表when,它们将被有效地or编辑在一起:

case response
  when "a","A"
    puts "ok"
  when "b","B"
    puts "awesome."
  else
    puts "I'm sorry. I did not get that.  Please try again."
end

对于忽略字母大小写的具体情况,您还可以在测试之前转换为上限或下限:

case response.upcase 
  when "A"
    puts "ok"
  when "B"
    puts "awesome."
  else
    puts "I'm sorry, I did not get that.  Please try again."
 end