Why Doesn't fmt.Scanf Always Wait for User Input in Go?

Understanding the Issue with fmt.Scanf in Go

In Go, the fmt.Scanf function allows you to read user input and store it in specified variables. However, sometimes users encounter a problem where fmt.Scanf doesn't wait for user input after the first scan and immediately moves on to subsequent prompts.

Explanation

In Go, fmt.Scanf reads characters from standard input up to the first delimiter (typically a newline). In earlier versions of Go, it did not consider a carriage return (r) followed by a newline (n) as a valid delimiter on Windows systems. This caused fmt.Scanf to end prematurely after reading the first character entered by the user.

Workaround

To resolve this issue, a simple workaround is to explicitly use the n delimiter in the format string passed to fmt.Scanf. For instance:

var inputSquare float64
fmt.Scanf("%f\n", &inputSquare)

By including the n in the format string, you tell fmt.Scanf to wait for a newline before considering the input complete. This ensures that the program pauses until the user presses Enter and completes their input.

User Input Validation

To validate user input for integers, you can use the strconv.ParseInt function, which checks if the entered string can be parsed into an integer and returns any errors encountered. For example:

inputSquare, err := strconv.ParseInt(inputSquareString, 10, 64)
if err != nil {
    // Handle error
}

Conclusion

By using the aforementioned technique, you can effectively address the issue of fmt.Scanf not waiting for user input in Go and implement proper input validation for integers.

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