puts "Input a number"
A = gets.try(&.to_i) || 0
puts "Ok now another number"
B = gets.try(&.to_i) || 0
def main
puts "Value of multiplication is #{A} * #{B}, Which equals = #{A * B}"
puts "Value of addition is #{A} + #{B}, Which equals = #{A + B}"
puts "Value of division is #{A} / #{B}, Which equals = #{A / B}"
puts "Value of minus is #{A} - #{B}, Which equals = #{A - B}"
puts "Value of modulus is #{A} % #{B}, Which equals = #{A % B}"
end
main
我想知道从Crystal中获取整数用户输入的最简单方法是什么?类似于Ruby的gets.chomp.to_i
要获得用户输入,您必须了解gets
的工作原理。当用户输入内容时它将返回String
,或者当用户没有输入任何内容时返回nil
(例如用户按下ctrl + C)。
在Ruby中如果你这样做:
x = gets.chomp.to_i
并运行它,但按ctrl + C你会在屏幕上打印出一个丑陋的异常。也许这是可以接受的,但这是Crystal不会轻易传递的东西,因为Crystal是类型安全的,你将不得不处理这种情况。也许你想为用户打印一些不错的东西而不是例外?
这里解释了如何处理Nil
:https://crystal-lang.org/api/0.25.1/Nil.html
例如,您可以这样做:
a = gets
if a # if a is a String
a = a.chomp.to_i # turn it into an integer
else
exit # just silently quit the program
end
另一种方法是使用to_nil!
,如果值为nil
,它将基本上引发异常:
a = gets.not_nil!.chomp.to_i
这与Ruby更相似,因为当用户使用ctrl + C退出时,您将在控制台中显示异常。关键的区别在于Crystal让你知道(通过nil
)这种可能性会发生,你应该选择在这种情况下做什么。
有更多方法可以处理这种情况(如其他评论中建议的try
解决方案),具体取决于您希望代码的简洁程度。
更接近Ruby的最后一个替代方案是使用read_line
,如果没有输入则会提升,所以你可以这样做:
a = read_line.chomp.to_i
(虽然在我的实验中,它现在似乎没有提高,我不知道为什么,可能是一些错误...)
这将执行您想要的操作,以便程序在用户为您提供有效的int之前不会继续。如果您只想简单地抛出错误,那么您不需要循环或try-catch语句。
while true
puts "give me a valid int:"
begin
i = gets.not_nil!.to_i
break
rescue
puts "that wasn't a valid int."
end
end
puts "you gave me: #{i}"
这里有两种解决方法:
粗糙的方式:
print "Input a number: "
a = gets
print "now another number: "
b = gets
begin
a = a.not_nil!.to_i
b = b.not_nil!.to_i
puts "Value of multiplication is #{a} * #{b}, Which equals = #{a * b}"
puts "Value of addition is #{a} + #{b}, Which equals = #{a + b}"
puts "Value of division is #{a} / #{b}, Which equals = #{a / b}"
puts "Value of minus is #{a} - #{b}, Which equals = #{a - b}"
puts "Value of modulus is #{a} % #{b}, Which equals = #{a % b}"
rescue e : Exception
puts sprintf "error: input a or b is invalid: a = %s, b = %s", a, b
end
正常方式:
def input(input : String) : Int
value = 0
loop do
print input
begin
a = gets
value = a.to_s.to_i # Force convert (String | Nil) to String then Int32.
break
rescue
# do nothing
end
end
value
end
a = input "Input a number: "
b = input "now another number: "
puts "Value of multiplication is #{a} * #{b}, Which equals = #{a * b}"
puts "Value of addition is #{a} + #{b}, Which equals = #{a + b}"
puts "Value of division is #{a} / #{b}, Which equals = #{a / b}"
puts "Value of minus is #{a} - #{b}, Which equals = #{a - b}"
puts "Value of modulus is #{a} % #{b}, Which equals = #{a % b}"