Question

I’m trying to verify that a character input to a double variable is of the right data type.

double number = 0;
int validCheck = 0;
char another = 'y';

while(another == 'y')
{
    cout<<"Please enter a number: ";
    validCheck = scanf("%lf", &number);

    while (validCheck !=1)
    {
        cout<<"Invalid input, please enter a number: ";
        validCheck = scanf("%lf", &number);
    }

When I compile this, it works fine provided I give a valid input, and an invalid input does put it into the while loop, but rather than checking for another input, it just spams my console with “Invalid input, please enter a number:” without even asking for a new input. What am I missing?

Answer 1

The invalid input remains in the input buffer, so the scanf is always presented with the same malformed input. You need to clear the input buffer, e.g.

int c;
do {
    c = getchar();
}while(c != '\n' && c != EOF);