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    <p>You asked a lot.</p> <p>You want to validate user input. Users should not be able to enter huge numbers, non-integers, and so on.</p> <p>I'm going to start off by answering that <strong>this is absolutely not a scenario that exceptions should be used for.</strong> Exceptions are used to handle <strong>exceptional</strong> circumstances. These are ones you can't anticipate or really deal with.</p> <p>A user enters a number that's too big? You can handle that. Tell them that their number is too big, please enter a number between 1 and X.</p> <p>A user enters the word apple? You can handle that. Tell them that they can only enter integers.</p> <p>One way of doing this would be to make a <code>ValidateInput</code> function. You can have it return a number (or an enum, they're basically the same thing) to tell you whether there was an error.</p> <p>In order to do the validation, you will most likely have to receive input as an <code>std::string</code> and then validate it before turning it into a number. Getting input as an <code>unsigned int</code> or similar integral type doesn't really allow you to check for errors.</p> <p>This adds a bit of work, since you need to manually validate the input manually. There are libraries with functions to help with this, such as <code>boost::lexical_cast</code>, but that's probably too much for you right now.</p> <p>Below is some very basic psuedo code to illustrate what I mean. It's only meant to give you an idea of what to do, it won't compile or do the work for you. You could extend it further by making a generic function that returns a message based on an error code and so on.</p> <pre><code>enum error_code { SUCCESS, // No error OUT_OF_RANGE, // Out of the range specified by the user INCORRECT_VALUE, // If user input "one" instead of 1 RANGE_SIGNED, // If user inputs a signed value for range NUM_LIMITS // Number exceeds unsigned long long }; // This function will check if the input is valid. // If it's not valid, it will return an error code to explain why it's invalid. error_code ValidateInput(const std::string&amp; input) { // Check if input is too large for an unsigned long long if (InputIsTooLarge) return NUM_LIMITS; // Check if input is negative if (InputIsNegative) return RANGE_SIGNED; // Check if input is not an integer if (InputIsNotInteger) return INCORRECT_VALUE; // If we make it here, no problems were found, input is okay. return SUCCESS; } unsigned long long GetInput() { // Get the user's input std::string input; std::cin &gt;&gt; input; // Check if the input is valid error_code inputError = ValidateInput(input); // If input is not valid, explain the problem to the user. if (inputError != SUCCESS) { if (inputError == NUM_LIMITS) { std::cout &lt;&lt; "That number is too big, please enter a number between " "1 and X." &lt;&lt; std::endl; } else if (inputError == RANGE_SIGNED) { std::cout &lt;&lt; "Please enter a positive number." &lt;&lt; std::endl; } else if (inputError == INCORRECT_VALUE) { std::cout &lt;&lt; "Please enter an integer." &lt;&lt; std::endl; } else { std::cout &lt;&lt; "Invalid input, please try again." &lt;&lt; std::endl; } // Ask for input again return GetInput(); } // If ValidateInput returned SUCCESS, the input is okay. // We can turn it into an integer and return it. else { return TurnStringIntoBigInt(input); } } int main() { // Get the input from the user unsigned long long number = GetInput(); // Do something with the input } </code></pre>
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    1. POConfusion about correct design of a program C++
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    1. USCollin Dauphinee
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    1. COIf exceptions can't be anticipated or dealt with, why does the language have a `catch` keyword?
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    2. COA fair question but a bit vague. Here, read this. http://www.boost.org/community/error_handling.html
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    3. COIs that the best way to create an interactive program?
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