scanf() does not have a simple method to meet OP’s goal.
Recommend using fgets() for input and then parse the string.
char buf[20];
fgets(buf, sizeof buf, stdin); // Could add check for NULL here
To limit to 2 decimal places, code could read the number in parts: integer portion and fraction, then form the result:
long long ipart;
unsigned d[2];
int n;
if (sscanf(buf, "%lld.%1u%1u %n", &ipart, &d[0], &d[1], &n) != 3 || buf[n]) {
Handle_InvalidInput();
}
double value = (d[0]*10 + d[1])/100.0;
value = ipart + ipart < 0 ? -value : value;
Even though this fulfills OP’s quest, I do not think it solves OP’s larger goal. So rather than limit input, read the input and then qualify it:
double value;
if (sscanf(buf, "%lf %n", &value, &n) != 1 || buf[n]) {
Handle_InvalidInput();
}
double rounded_value = round(value * 100.0)/100.0;
if (rounded_value != value) {
Handle_OverlyPreciseNumber(value, rounded_value);
}
Other more pedantic methods would inspect the string buf for ddd…ddd.dd syntax, etc. But the issue is clear: read the data and then qualify the data read. Do not attempt to restrict the input.