Switch Statements

Switch Statement Often you want to do a series of tests –if i==0 … else if i==1 …. else if i==2 … else if i==3 …. C++ provides the switch statement to help in this situation –It allows you to specify a large set of cases you want to be able to match, yet works efficiently to find and execute the particular case matched

Format Format: switch (switchExpression ) { case value1: statements; break; case value2: statements; break; … default: statements; } Example: ………… int mortgageTerm; float interestRate; cin>> mortgageTerm; Switch (mortgageTerm) { case 10: interestRate= 3.0; break; case 15: interestRate=3.5; break; case 30: interestRate=4.0; break; default: cout<<“please enter a valid loan term”; }

char grade; cin >> grade; switch (grade) { case 'A': cout << "Great job!!"; break; case 'B': cout << "Good job"; break; case 'C': cout << "Satisfactory job"; break; case 'D': cout << "Hmmm... need to work a little harder"; break; case 'F': cout << "Sorry, you failed the class"; break; default: cout << "The letter you typed " << grade << " is not a valid grade"; } Examples

Examples: #include using namespace std; int main() { int operand1 = 0, operand2 = 0, result=0; char operator = ‘ ‘; cout << “Please enter expression (num oper num) ? “; cin >> operand1 >> operator >> operand2; switch (operator) { case ‘+’: result = operand1 + operand2; break; case ‘-’: result = operand1 - operand2; break; // other cases left off for room default: cout << “Did not recognize operator” << endl; } cout << operand1 << “ “ << operator << “ “ <<operand2 << “ = “ << result << endl; return 0; }

Examples int x, y; cin>>x>>y; switch (x>y) { case 0: cout<<“x is no greater than y”; break; case 1: cout<<“ x is greater than y”; break; default: } int x, y; cin>>x>>y; switch (x>y) { case false: cout<<“x is no greater than y”; break; case true: cout<<“ x is greater than y”; break; default: }

Fall Through Example: …. switch (flight_class) { case 3: ticket=300; case 2: ticket=500; case 1: ticket=1000; } cout<<“you need to pay”<<“\” ticket <<“dollars, thank you!”<<endl; What the third class passenger will need to pay? Switch (flight_class) { Case 3: ticket=300; break; Case 2: ticket=500; break; Case 1:ticket=1000; break; Default: cout<<“unknown class!”; }

Exercise Convert the following segment of code to switch statement: int j, n; ….. If (j==3 || j==5) n = 6; else if ( j==4 || j==8) n = 9; else if (j==2) n = 8; else n=0;

Exercise: What the output will be? #include using namespace std; int x=1, y=2, z=3; int main(){ switch (x>0) { case 1: switch (y<0) { case 1: cout<<“?”; break; case 2: cout<<“%”; break; } case 0: switch (z==3) { case 0: cout<<“+”; break; case 1: cout<<“#”; break; } default: cout<<“&”; } return 0; }

Switch Statement Style ideas for the switch statement –Unless you have many conditions (4 or more), use if-else-if instead of switch –Always provide a default case – if you are pretty sure you have all cases covered, putting an error message in the default is good to identify unexpected errors –Order the cases in some logical order (numeric, alphabetic) –Keep the size of each of the cases small If you have to do lots of work in each case, call a function from inside the case