CSC 107 – Programming For Science

Today’s Goal  Know how to write selections besides if-else  When each of the options makes sense  When each selection statements should NOT be used  How to covert between them

Press “*” For Horrible Music  Writing software for voic system  Which of 12 buttons hit determine action to take  For much of time, many keys have same effect  Long, ugly if-else if-else statement results  Now imagine choosing from 256 options  Required for web browsers & other systems  Takes forever to write & code impossible to read

Press “*” For Horrible Music  Writing software for voic system  Which of 12 buttons hit determine action to take  For much of time, many keys have same effect  Long, ugly if-else if-else statement results  Now imagine choosing from 256 options  Required for web browsers & other systems  Takes forever to write & code impossible to read

Long if-else statement if (keyHit == 1) { cout << “Please say message to record”; } else if (keyHit == 2) { cout << “Skipping to next message”; } else if (keyHit == 3) { cout << “Playing first new message”; } else if (keyHit == 4) { cout << “Message is saved for 30 days.”; } else if (keyHit == 6) { cout << “Message deleted”; } else if (keyHit == 7) { cout << “dniwer egasseM “; } else if ((keyHit == 5) || (keyHit == 8)) { cout << “I’m sorry Dave, I can’t do that.”; } else { cout << “The hit squad will find you soon.”; }

Long if-else statement if (keyHit == 1) { cout << “Please say message to record”; } else if (keyHit == 2) { cout << “Skipping to next message”; } else if (keyHit == 3) { cout << “Playing first new message”; } else if (keyHit == 4) { cout << “Message is saved for 30 days.”; } else if (keyHit == 6) { cout << “Message deleted”; } else if (keyHit == 7) { cout << “gnidniwer egasseM “; } else if ((keyHit == 5) || (keyHit == 8)) { cout << “I’m sorry Dave, I can’t do that.”; } else { cout << “The hit squad will find you soon.”; }

Better idea: if (keyHit == 1) { cout << “Please say message to record”; } else if (keyHit == 2) { cout << “Skipping to next message”; } else if (keyHit == 3) { cout << “Playing first new message”; } else if (keyHit == 4) { cout << “Message is saved for 30 days.”; } else if (keyHit == 6) { cout << “Message deleted”; } else if (keyHit == 7) { cout << “dniwer egasseM “; } else if ((keyHit == 5) || (keyHit == 8)) { cout << “I’m sorry Dave, I can’t do that.”; } else { cout << “The hit squad will find you soon.”; }

Better idea: switch Statement switch (keyHit) { case 1: cout << “Please say message to record”; break; case 2: cout << “Skipping to next message”; break; case 3: cout << “Playing first new message”; break; case 4: cout << “Message will be saved for 30 days.”; break; case 6: cout << “Message deleted”; break; case 7: cout << “gnidniwer egasseM”; break; case 5: case 8: cout << “I’m sorry Dave, I can’t do that.”; break; default: cout << “The hit squad will find you soon.”; }

Better idea: switch Statement switch (keyHit) { case 1: cout << “Please say message to record”; break; case 2: cout << “Skipping to next message”; break; case 3: cout << “Playing first new message”; break; case 4: cout << “Message will be saved for 30 days.”; break; case 6: cout << “Message deleted”; break; case 7: cout << “dniwer egasseM”; break; case 5: case 8: cout << “I’m sorry Dave, I can’t do that.”; break; default: cout << “The hit squad will find you soon.”; }

Better idea: switch Statement switch (keyHit) { case 1: cout << “Please say message to record”; break; case 2: cout << “Skipping to next message”; break; case 3: cout << “Playing first new message”; break; case 4: cout << “Message will be saved for 30 days.”; break; case 6: cout << “Message deleted”; break; case 7: cout << “dniwer egasseM”; break; case 5: case 8: cout << “I’m sorry Dave, I can’t do that.”; break; default: cout << “The hit squad will find you soon.”; }

Outline of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : case label n+1 : statement;... break;... default: statement;... }

Outline of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : case label n+1 : statement;... break;... default: statement;... } Anything of ordinal (whole number) type

Outline of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : case label n+1 : statement;... break;... default: statement;... } Labels must be constant or literal

Outline of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : case label n+1 : statement;... break;... default: statement;... } This is legal; execution only stops at break or ending brace

Outline of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : statement; statement; case label n+1 : statement;... break;... default: statement;... } Still legal; execution only stops at break or ending brace

Outline of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : case label n+1 : statement;... break;... default: statement;... } Optional, like else must be at end & matches anything left

Execution of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : case label n+1 : statement;... break;... default: statement;... } Same as equality test in if : if (expression == label 1 ) {

Execution of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : case label n+1 : statement;... break;... default: statement;... } Works like OR (||) in if-else if : else if (expression == label n || expression == label n+1 ) {

Execution of switch statement switch (expression) { case label 1 : statement; statement;... break;... case label n : statement; statement; case label n+1 : statement;... break;... default: statement;... } Fall-thru unique to switch; Cannot overlap in if-else if

switch Statement  Depends on a value to determine what is run  Easier to read than if-else if  Expression can be anything you want  bool, char, short, int, or long result required  Where execution starts marked by the labels  Literals or constants only usable for the labels  Labels in any order: starts at first equal to value  Doesn’t stop at next label (not like if-else s)  Execution will only stop at closing brace or break

Executing switch Statement 1. Evaluates expression 2. Tries to find matching case or default  If no default no match, will skip past switch 3. Execution starts at 1 st matching label  Execution will continue until break; found  Continues into next case if break; is not hit 4. Restarts running after switch once break hit  Legal to reach end of switch without a break  Continues running code after switch

Tracing switch Statement float temp = -40; float convert; char c; cin >> c; switch (toupper(c)) { case ‘K’: temp = temp – ; case ‘C’: convert = ((temp / 5) * 9) + 32; break; case ‘F’: convert = ((temp - 32) / 9) * 5; break; default: cout << “Amoronsayswhat?” << endl; } cout <<“Converted temp: ” << convert << endl;

Tracing switch Statement float temp = -40; float convert; char c; cin >> c; switch (toupper(c)) { case ‘K’: temp = temp – ; case ‘C’: convert = ((temp / 5) * 9) + 32; break; case ‘F’: convert = ((temp - 32) / 9) * 5; break; default: cout << “Amoronsayswhat?” << endl; } cout <<“Converted temp: ” << convert << endl;

Tracing switch Statement float temp = -40; float convert; char c; cin >> c; switch (toupper(c)) { case ‘K’: temp = temp – ; case ‘C’: convert = ((temp / 5) * 9) + 32; break; case ‘F’: convert = ((temp - 32) / 9) * 5; break; default: cout << “Amoronsayswhat?” << endl; } cout <<“Converted temp: ” << convert << endl;

Steel Cage Match if - else switch  Actions cannot overlap  Expression per if, else if  Any boolean expressions  else gets remaining cases only when expression(s) are true  Use for actions needed only when expression(s) are true  Overlap by omitting break;  Evaluates single expression  Only 1 equality test  default gets all other cases when expression has specific value actions should overlap  Use for actions needed when expression has specific value –or – actions should overlap

Your Turn  Get in groups of 3 & work on following activity

For Next Lecture  Read sections 2.1 – 2.9 for Tuesday  How should we write programs?  Is there some way to make debugging less painful?  Why should we not always rush to the computer?  Week #4 weekly assignment available on Angel  If problem takes more than 10 minutes, TALK TO ME!  Programming Project #1 available on Angel also  One of term’s 3 large assignments – due Oct. 7