Validate Float Logic?

[Bajanine]

I spent the evening trying to figure a good way to validate user input of a floating point number from a string . The following code snippet works, but seems complicated to me. I am sure there is probably a more efficient way. If so could someone please give me some constructive criticism or pointers.

////////////////////////////////////
// Validate floating point number.//
////////////////////////////////////

int Decimal = 0;

for (int i = 0; i < nLen; i++ )
{
if ( !isdigit(pbuffer[i]))
{
		if ( Decimal == 0 )
		{
			if( pbuffer[i] == '.' )
			{
				Decimal = 1;
				continue;
			}
		}
		MessageBox (NULL, TEXT ("Enter a floating point number."), 
			TEXT ("Invalid input!"), MB_ICONINFORMATION) ;
		return TRUE;	// break out of switch statement.
}
}

// pbuffer is valid so do calculations.