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Lecture 7: if-else if-else Statements

CSC 107 – Programming For Science. Lecture 7: if-else if-else Statements. if (…) statement. First evaluates expression in parenthesis If expression is true , executes next statement Skips over the statement , when expression is false

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Lecture 7: if-else if-else Statements

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  1. CSC 107 – Programming For Science Lecture 7:if-else if-else Statements

  2. if (…) statement • First evaluates expression in parenthesis • If expression is true, executes next statement • Skips over the statement, when expression is false inthst = 30, dc = 27;bool gang = (hst > 12) && (dc == 27); if (nyc == dc)cout << “You lie" << endl;if (!gang)cout << "That ain't right." << endl;if (dc > 20);cout << "Huh?"

  3. if (…) statement • First evaluates expression in parenthesis • If expression is true, executes next statement • Skips over the statement, when expression is false • This leads to one very common bug • ;is statement (a boring statement, but…) if (dc > 20);cout << "Huh?"

  4. I Want More! • Add opening brace ({) after closing parenthesis • Can now write all statements to execute • Add closing brace (}) to show where ifends • If expression false, execution restarts at that point if (sqrt(x) == 3.0) {cout << "root of x = 3" << endl; cout << "So, x = 9" << endl;}

  5. true false else statement • Often want to perform one of two actions • Execute some statements when condition is true • But when it is false, do some other work • Continue as normal afterward,no matter the path • In these cases, can use if-else statement • elsemust come immediately after if's ; or } • Like if, elseshould always have {} • Cannot have elsewithout ifto start process • In C++, there is no problem with if & no else

  6. if - else Examples if (value > 0) {cout << "Its positive" << endl;} else { value = abs(value);}if ((year % 4 == 0) && ((year % 100) != 0)) {daysInYear = 366;cout << "Not quite right, but close enough";cout << endl;leapYear = true;} else {leapYear = false;daysInYear = 365; }

  7. Many Choices • May want to choose from many possibilities

  8. Many Choices • May want to choose from many possibilities • Could nest if – elsestatements inside one another if (a > 3) {cout << "a greater than 3" << endl;} else { if (b > 10) {cout << "b greater than 10" << endl; } else { if (c == -23) {cout << "c is equal to -23" << endl; } else {cout << "This really sucks" << endl;cout << "Sorry its stupid" << endl; } }}

  9. Many Choices • May want to choose from many possibilities • Could nest if – elsestatements inside one another • Or easier & nicer if – else if – else statement if (a > 3) {cout << "a greater than 3" << endl;} else if (b > 10) {cout << "b greater than 10" << endl;} else if (c == -23) {cout << "c is equal to -23" << endl;} else {cout << "This really sucks" << endl;cout << "Sorry its stupid" << endl;}

  10. if – else if – else Usage • Must begin with ifstatement at the start • This is required; what would we be saying elseto? • Onlyrequired part of this entire process • Can then have zero or more else ifs • Tests can be anything; do not have to be related • Until one is true, will be examined one-by-one • Execute 1st clause where true expression is found • Only at the very end can have else clause • If nothing else matches then elseis executed

  11. if – else if – else Example if (wealth > 1000000) {cout << "Can I borrow a buck?" << endl;} else if (wealth > 100000) {cout << "Wow, you're comfortable" << endl;} else {cout << "Government bailout!" << endl;} else if (wealth > -100000) {cout << "File for bankruptcy" << endl;} else if (wealth > 10000) {cout << "Could be worse" << endl;} else if (wealth > 0) {cout << "Good luck" << endl;}

  12. if – else if – else Example if (wealth > 1000000) {cout << "Can I borrow a buck?" << endl;} else if (wealth > 100000) {cout << "Wow, you're comfortable" << endl;} else {cout << "Government bailout!" << endl;} else if (wealth > -100000) {cout << "File for bankruptcy" << endl;} else if (wealth > 10000) {cout << "Could be worse" << endl;} else if (wealth > 0) {cout << "Good luck" << endl;}

  13. if – else if – else Example if (wealth > 1000000) {cout << "Can I borrow a buck?" << endl;} else if (wealth > 100000) {cout << "Wow, you're comfortable" << endl;} else if (wealth > -100000) {cout << "File for bankruptcy" << endl;} else if (wealth > 10000) {cout << "Could be worse" << endl;} else if (wealth > 0) {cout << "Good luck" << endl;} else {cout << "Government bailout!" << endl;}

  14. if – else if – else Example if (wealth > 1000000) {cout << "Can I borrow a buck?" << endl;} else if (wealth > 100000) {cout << "Wow, you're comfortable" << endl;} else if (wealth > -100000) {cout << "File for bankruptcy" << endl;} else if (wealth > 10000) {cout << "Could be worse" << endl;} else if (wealth > 0) {cout << "Good luck" << endl;} else {cout << "Government bailout!" << endl;}

  15. if – else if – else Example if (wealth > 1000000) {cout << "Can I borrow a buck?" << endl;} else if (wealth > 100000) {cout << "Wow, you're comfortable" << endl;} else if (wealth > 10000) {cout << "Could be worse" << endl;} else if (wealth > 0) {cout << "Good luck" << endl;} else if (wealth > -100000) {cout << "File for bankruptcy" << endl;} else {cout << "Government bailout!" << endl;}

  16. Spacing in a Program • C++ ignores spaces in a program • This also means where newlines placed ignored • #define & text in quotes major exceptions to rule • This can lead to interesting code choices

  17. Coding Style • Use consistent size to indent (I use 2 spaces) • Not required, but makes it much easier to read code • Indent code within braces ({}) to show structure • If line could or does contain { add to indentation • Decrease indentation each }should be on a line • if,else if, or elseline has opening brace • Always use braces to prevent having to fix bugs • Limit space, closing brace on else/else if line • Closing brace on own line otherwise (like at end)

  18. Coding Style Example #include <iostream>using namespace std;int main(void) {intdcScore = 27, hstScore = 30; if (dcScore > hstScore) {cout << "Prof. Hertz happy" << endl;cout << "His team won" << endl; } else {cout << "His team lost." << endl;cout << "He is sad";dcScore += 100;if (dcScore < hstScore) {cout << "Ouch. That's bad." <<endl;} } cout << "And now code continues" << endl; return 0;}

  19. Coding Style Example #include <iostream>using namespace std;int main(void) {intdcScore = 27, hstScore = 30; if (dcScore > hstScore) {cout << "Prof. Hertz happy" << endl;cout << "His team won" << endl; } else {cout << "His team lost." << endl;cout << "He is sad";dcScore += 100;if (dcScore < hstScore) {cout << "Ouch. That's bad." <<endl;} } cout << "And now code continues" << endl; return 0;}

  20. Coding Style Example #include <iostream>using namespace std;int main(void) {intdcScore = 27, hstScore = 30; if (dcScore > hstScore) {cout << "Prof. Hertz happy" << endl;cout << "His team won" << endl; } else {cout << "His team lost." << endl;cout << "He is sad";dcScore += 100;if (dcScore < hstScore) {cout << "Ouch. That's bad." <<endl;} } cout << "And now code continues" << endl; return 0;}

  21. Coding Style Example #include <iostream>using namespace std;int main(void) {intdcScore = 27, hstScore = 30; if (dcScore > hstScore) {cout << "Prof. Hertz happy" << endl;cout << "His team won" << endl; } else {cout << "His team lost." << endl;cout << "He is sad";dcScore += 100;if (dcScore < hstScore) {cout << "Ouch. That's bad." <<endl;} } cout << "And now code continues" << endl; return 0;}

  22. Coding Style Example #include <iostream>using namespace std;int main(void) {intdcScore = 27, hstScore = 30; if (dcScore > hstScore) {cout << "Prof. Hertz happy" << endl;cout << "His team won" << endl; } else {cout << "His team lost." << endl;cout << "He is sad";dcScore += 100;if (dcScore < hstScore) {cout << "Ouch. That's bad." <<endl;} } cout << "And now code continues" << endl; return 0;}

  23. Coding Style Example #include <iostream>using namespace std;int main(void) {intdcScore = 27, hstScore = 30; if (dcScore > hstScore) {cout << "Prof. Hertz happy" << endl;cout << "His team won" << endl; } else {cout << "His team lost." << endl;cout << "He is sad";dcScore += 100;if (dcScore < hstScore) {cout << "Ouch. That's bad." <<endl;} } cout << "And now code continues" << endl; return 0;}

  24. Your Turn • Get in groups of 3 & work on following activity

  25. For Next Lecture • Read sections 7.4, 7.6 – 7.7 for Thursday • What if we want to run multiple clauses? • Is something easier for testing lots of equality? • How can we breaklots of things? • Week #3 weekly assignment due today • If problem takes more than 10 minutes, TALK TO ME! • Week #4 weekly assignment also on Angel

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