Switch Statements

1. Switch Statements

2. 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

3. Format 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”; } • Format: • switch(switchExpression ){ • case value1: • statements; • break; • case value2: • statements; • break; • … • … • default: • statements; • }

4. Examples 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"; }

5. Examples: #include <iostream> 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; }

6. Examples 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: } 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: }

7. Fall Through Example: Switch (flight_class) { Case 3: ticket=300; break; Case 2: ticket=500; break; Case 1:ticket=1000; break; Default: cout<<“unknown class!”; } …. 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?

8. 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;

9. Exercise: What the output will be? #include <iostream> 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; }

10. 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