输入C，C ++，cin，scanf输入错误

Question

Im a total beginner in C and here is my problem. In C++ I would look for bad input(not unsigned int) this way:

long double c;
cin >> c;

if (c == (unsigned int) c) {
cout<<"OK";    
}
else
cout<<"NOT OK";

However when now learning C I'm trying to do it the same way, but it does not work:

long double c;
scanf("%lf", &c);

if (c == (unsigned int) c) {
printf("OK\n");    
}
else
printf("NOT OK\n");    

Any advice on how to fix it? My task is to do this by just using scanf and no strings. I don't want negative and float numbers to be inputted. Why doesnt this work?

Answer 1

The conversion directive %lf is for scanning double s.

To scan long double s, use %Lf , with an upper case L .

From the specification of fscanf (7.21.6.2)

l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to long int or unsigned long int ; that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to double ; or that a following c, s, or [ conversion specifier applies to an argument with type pointer to wchar_t .

L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer to long double .