# Setting a User Input to a Double (Or a Specific Data Type)

**URL:** <https://discuss.kotlinlang.org/t/setting-a-user-input-to-a-double-or-a-specific-data-type/4082>\
**Category:** Language Design\
**Created:** [August 8, 2017, 3:34pm UTC](https://discuss.kotlinlang.org/t/setting-a-user-input-to-a-double-or-a-specific-data-type/4082 "2017-08-08T15:34:16Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![alanfo](https://avatars.discourse-cdn.com/v4/letter/a/bbe5ce/32.png) [@alanfo](https://discuss.kotlinlang.org/u/alanfo)\
**Post date:** [August 8, 2017, 4:22pm UTC](https://discuss.kotlinlang.org/t/setting-a-user-input-to-a-double-or-a-specific-data-type/4082/2 "2017-08-08T16:22:37Z")

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Try this instead which checks that what you’re entering is a valid number and, if it isn’t, asks you to reinput it:

```auto
    var originalTotal: Double?

    do {
       print("Enter the original total : ")
       originalTotal = readLine()!!.toDoubleOrNull()
       if (originalTotal == null) println("Not a valid number, try again")
    }
    while (originalTotal == null)

    var tip = 0.15 * originalTotal
    println("Your tip is : $tip")
    var total = originalTotal + tip
    println("Your total is : $total")

```

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_[View the full topic](https://discuss.kotlinlang.org/t/setting-a-user-input-to-a-double-or-a-specific-data-type/4082)._