How to Properly Validate Double User Input in C ?

Validating User Input as a Double in C

Ensuring user input accuracy is crucial when working with numerical data. This article explores how to effectively validate user input as a double in C .

Understanding the Problem:

The provided code attempts to validate user input as a double. However, it fails to prompt for subsequent inputs if the input is invalid, resulting in an infinite loop of error messages.

Solution:

To address this issue, it is necessary to clear the error state and discard any invalid characters entered previously. This can be achieved using the following code:

while (1) {
  if (cin >> x) {
      // valid number
      break;
  } else {
      // not a valid number
      cout << "Invalid Input! Please input a numerical value." << endl;
      cin.clear();
      while (cin.get() != '\n') ; // empty loop
  }
}

In this modified code:

• cin.clear(): Clears the error state.
• while (cin.get() != 'n') ;: Discards all invalid characters entered on the previous line. This loop continues until the newline character ('n') is encountered, effectively emptying the input buffer.

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