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With string validation, we accept all user input as a string, and then accept or reject that string depending on whether it is formatted appropriately.

For example, if we ask the user to enter a telephone number, we may want to ensure the data they enter has ten digits.

If our input was valid, gcount() should return 1 (the newline character that was discarded).

If it returns more than 1, the user entered something that wasn’t extracted properly, and we should ask them for new input.

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2) If you don’t want this to be valid input, it is not rejected (and you have garbage in your stream). This is easy: If you don’t want such input to be valid, we’ll have to do a little extra work.

With numerical validation, we are typically concerned with making sure the number the user enters is within a particular range (eg. However, unlike with string validation, it’s possible for the user to enter things that aren’t numbers at all -- and we need to handle these cases too.

To help us out, C provides a number of useful functions that we can use to determine whether specific characters are numbers or letters.

Although these flags live in ios_base, because ios is derived from ios_base and ios takes less typing than ios_base, they are generally accessed through ios (eg. ios also provides a number of member functions in order to conveniently access these states: Note that this program is expecting the user to enter an integer.

However, if the user enters non-numeric data, such as “Alex”, cin will be unable to extract anything to n Age, and the failbit will be set.

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