1. CSC 107 – Programming For Science

2. Final Exams Dec. 16, 8AM – 10AM in OM221  Exam for CSC107: Dec. 16, 8AM – 10AM in OM221  Will be done using paper & pencil in classroom  Open-note & open-book so bring your cheatsheets  Problem on exam will be similar to midterms Dec. 14, 9:00 – 10:00 Dec. 14, 10:15 – 11:15  Mastery Exam: Dec. 14, 9:00 – 10:00 (if lab on Thurs ) Dec. 14, 10:15 – 11:15 (if lab on Tues )  Given in OM115 and will be programming w/ Eclipse  Open-note & open-book so bring your cheatsheets  Halfway between labs & weekly assignments problems  Will have chance to practice in lab next week

3. Today’s Goal  Review effects of #define s statements  How we can use these to create symbolic constants  Use of symbolic constants & how differ from variables  Discuss how to use #define for C++ macros  Parameter meaning within macro & potential errors  Within the macro what are the limits on code & use  Discuss compact if-else ( ? : ) & see how it works  Examine problems with it & why its rarely used  Compare macros & functions within C++

4. Symbolic Constants  Directive can be used to name a constant  Any/all lines BELOW directive can use this constant  Pre-processor replaces name with value  Compiler sees value as if that were written there  When reading the code, programmer sees name  Makes code much easier to read, write, debug  Names traditionally in all CAPITAL letters  THIS IS NOT REQUIRED  THIS IS NOT REQUIRED, but “good style”

5. Symbolic Constants Use  Do not actually exist when program runs  Symbolic constants not allocated in stack or heap  Not just for constants: can be expressions or statements  Often in header files since used for vital information  Contents copy-and-pasted without investigating  Starts copying after it skips space(s) until line’s end not  Do not include equals sign ( = ) unless you want it copied no  Semicolons copied also, so no semicolons needed

6. What You Write And Work With #define PI 3.1415 #define AVOGADRO 6.022E23 #define R_SQUARED r * r #define DUMB_EXAMPLE “Matthew Hertz” double area = PI * (R_SQUARED); cout << R_SQUARED; cout << DUMB_EXAMPLE;

7. What The Compiler Sees #define PI 3.1415 #define AVOGADRO 6.022E23 #define R_SQUARED r * r #define DUMB_EXAMPLE “Matthew Hertz” double area = PI * (R_SQUARED); cout << R_SQUARED; cout << DUMB_EXAMPLE;

8. What The Compiler Sees #define AVOGADRO 6.022E23 #define R_SQUARED r * r #define DUMB_EXAMPLE “Matthew Hertz” double area = 3.1415 * (R_SQUARED); cout << R_SQUARED; cout << DUMB_EXAMPLE;

9. What The Compiler Sees #define AVOGADRO 6.022E23 #define R_SQUARED r * r #define DUMB_EXAMPLE “Matthew Hertz” double area = 3.1415 * (R_SQUARED); cout << R_SQUARED; cout << DUMB_EXAMPLE;

10. What The Compiler Sees #define R_SQUARED r * r #define DUMB_EXAMPLE “Matthew Hertz” double area = 3.1415 * (R_SQUARED); cout << R_SQUARED; cout << DUMB_EXAMPLE;

11. What The Compiler Sees #define DUMB_EXAMPLE “Matthew Hertz” double area = 3.1415 * (r * r); cout << r * r; cout << DUMB_EXAMPLE;

12. What The Compiler Sees double area = 3.1415 * (r * r); cout << r * r; cout << “Matthew Hertz”;

13. What The Compiler Sees double area = 3.1415 * (r * r); cout << r * r; cout << “Matthew Hertz”;

14. Macro Basis  C/C++ constructs similar to symbolic constants  (Mostly) Copy-and-paste contents within program  Within file can be used anywhere BELOW declaration  Line begins with #define & goes through lines end  But, unlike before, macros contain parameters  Replaced by arguments when pasted into program  Replacement performed by copy-and-pasting, also  No types required, since no memory used by params caveat emptor  Low-overhead, limited checks; caveat emptor

15. Writing Macros

16. Calling Macro From Program  Called like function & must match # of params  Can use any expression since will be copy-and-pasted  Low overhead makes their usage much looser  MUCH  MUCH harder to find & fix bugs with this  Compiler errors in macro will flagged on each call  May not be visible, since error could be in macro  Debugging also hard, since unclear where code exists

17. Coding With Macros #define IS_UPPER(c) (c >= ‘A’ && \ c <= ‘Z’) #define NEXT_WORD(rex) strchr(rex, ‘ ‘)+1 #define SQUARE(longP) (longP * longP) double b = 23; char rex[100] = “Censored censored”; int i = 12; if (IS_UPPER(rex[1])) { rex = NEXT_WORD(rex); } if (SQUARE(i) < 12) { cout << IS_UPPER(b) << SQUARE(rex); }

18. Coding With Macros #define IS_UPPER(c) (c >= ‘A’ && \ c <= ‘Z’) #define NEXT_WORD(rex) strchr(rex, ‘ ‘)+1 #define SQUARE(longP) (longP * longP) double b = 23; char rex[100] = “Censored censored”; int i = 12; if ((rex[1] >= ‘A’ && rex[1] <= ‘Z’)) { rex = NEXT_WORD(rex); } if (SQUARE(i) < 12) { cout << IS_UPPER(b) << SQUARE(rex); }

19. Coding With Macros #define IS_UPPER(c) (c >= ‘A’ && \ c <= ‘Z’) #define NEXT_WORD(rex) strchr(rex, ‘ ‘)+1 #define SQUARE(longP) (longP * longP) double b = 23; char rex[100] = “Censored censored”; int i = 12; if ((rex[1] >= ‘A’ && rex[1] <= ‘Z’)) { rex = strchr(rex, ‘ ‘) + 1; } if (SQUARE(i) < 12) { cout << IS_UPPER(b) << SQUARE(rex); }

20. Coding With Macros #define IS_UPPER(c) (c >= ‘A’ && \ c <= ‘Z’) #define NEXT_WORD(rex) strchr(rex, ‘ ‘)+1 #define SQUARE(longP) (longP * longP) double b = 23; char rex[100] = “Censored censored”; int i = 12; if ((rex[1] >= ‘A’ && rex[1] <= ‘Z’)) { rex = strchr(rex, ‘ ‘) + 1; } if ((i*i) < 12) { cout << IS_UPPER(b) << SQUARE(rex); }

21. Coding With Macros #define IS_UPPER(c) (c >= ‘A’ && \ c <= ‘Z’) #define NEXT_WORD(rex) strchr(rex, ‘ ‘)+1 #define SQUARE(longP) (longP * longP) double b = 23; char rex[100] = “Censored censored”; int i = 12; if ((rex[1] >= ‘A’ && rex[1] =‘A’&& b<=‘Z’) << (rex * rex); }

22. Coding With Macros #define IS_UPPER(c) (c >= ‘A’ && \ c <= ‘Z’) #define NEXT_WORD(rex) strchr(rex, ‘ ‘)+1 #define SQUARE(longP) (longP * longP) double b = 23; char rex[100] = “Censored censored”; int i = 12; if ((rex[1] >= ‘A’ && rex[1] =‘A’&& b<=‘Z’) << (rex * rex); }

23. Remember You See This Code… #define IS_UPPER(c) (c >= ‘A’ && \ c <= ‘Z’) #define NEXT_WORD(rex) strchr(rex, ‘ ‘)+1 #define SQUARE(longP) (longP * longP) double b = 23; char rex[100] = “Censored censored”; int i = 12; if (IS_UPPER(rex[1])) { rex = NEXT_WORD(rex); } if (SQUARE(i) < 12) { cout << IS_UPPER(b) << SQUARE(rex); }

24. Compact If-Else Operator  Macros often want to “return” result of if - else  Must compute in 1 expression; cannot use return  Luckily, C++ includes a really ugly hack for this

25. Compact If-Else Operator  Macros often want to “return” result of if - else  Must compute in 1 expression; cannot use return  Luckily, C++ includes a really ugly hack for this

26. Compact If-Else Operator  ?: operator is if - else computing a value (boolean expression) ? value if true : value if false #define POSITIVE(x) (x > 0) ? true : false; #define ROOT(x, y) (y == 0) ? 0 : pow(x,-y); int p = (pow(k, 2) < 10) ? pow(j,2) : 3;  Creates really hard to read & debug code  Use only when necessary, but occasionally helpful

27. Oops...  Care needed to protect arguments in macros  Copy-and-pasted  Copy-and-pasted, but by something with IQ of 0  Despite best of intentions, unseen bugs occur #define SUMSQUARE(a,b) a*a+b*b int x = 3, y = 4; cout << SUMSQUARE(2,4)<<endl; cout << SUMSQUARE(x,2)<<endl; cout << SUMSQUARE(4,y)<<endl; cout << SUMSQUARE(x,y)<<endl; cout << SUMSQUARE(x+1,y+3)<<endl; cout << SUMSQUARE(x++,++y)<<endl;

28. Protected Macros  Parenthesis are your friends, use them liberally  Use them to surround all uses of all params  Consider order of operations & how they can change #define SQR_U5(i) (((i)*(i))<5) int j = 2; double dbl = -3.0; SQR_U5(j); SQR_U5(dbl); SQR_U5(j-2); SQR_U5(dbl+2); SQR_U5(j+dbl);

29. Steel Cage Match FunctionMacro  Stands on own in program  Fixed types cannot change  Slight overhead per call  Results apparent & clear  Easy to find and debug  Useful nearly always  Must be pasted in function  Params untyped & flexible  No frame, so no cost to call  Murky effects go unseen  Often in header & impossible to fix tiny operations  Good for tiny operations

30. Your Turn  Get into your groups and try this assignment

31. For Next Lecture  Read Section 16.6 on recursion for Wednesday  What does it mean for function to be recursive?  How does recursion work & drawing traces this code  Why would we ever bother to use recursion in code?  Angel has Weekly Assignment #14 due tomorrow  Last project  Last project due on Friday