A safe-to-use, long-lasting switch statement should always contain a default label in order to avoid hard-to-detect bugs such as the following:
//Month.h fileenum Month { Jan, Feb, Mar, //...etc. Dec};//Month.cpp fileint daysInMonth(Month month) { int result = 0; switch (month) { case Jan: result = 31; break; case Feb: result = 28; break; //...Mar to Nov go here case Dec: result = 31; break; //no default } //end switch return result; }//end daysInMonth() Now suppose some other programmer needs to extend the Month enumeration later in the following manner:
//file Month.h re-edited enum Month { Jan, Feb, LeapFeb, //newly added Mar, //...etc. Dec};As a result, the switch statement above will return the wrong result; for example, 0, to its user’s amazement when its month is LeapFeb. Had a default label been used, this bug could have been detected easily:
switch (month) { //now with a default case Jan: result = 31; break; case Feb: result = 28; break; //...Mar to Nov go here case Dec: result = 31; break; deafult: cout<<"unsupported month value;check this switch!"; break; } //end switch
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