For example, illegal data might result in the maths processor being asked to calculate the square root of a negative quantity. The number of possible ways in which illegal data can be entered is also very large. To lay traps, deal safely with them all and inform the user, is impractical and will itself increase the liklihood of bugs remaining in the finished product. In G4FGQ's programs a bare minimum of protection is provided against entry of impossible data. Inevitably the user will make mistakes especially when unfamiliar with a new program.
Mistakes are most likely to occur when entering numerical values.
They fall into categories of incorrect measurement units, impossible physical proportions, ie, wire diameter greater than wire pitch, inclusion of non-numerical characters and using a comma for a decimal point. If you are running one of these programs in DOS where you have arrived via Windows, and it aborts, the system may not automatically switch you back into Windows. No harm is likely to come either to the computer or to the program as a result of being unceremoniously dumped back into the system. The .EXE ending may be omitted. If you are not in the same directory then the name of the program must be preceded by the directory path to the program, the several items being separated by backslashes.