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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.
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.