Final Exam

1. Final Exam • Final Exam: Thursday Dec 13th, 2001 at 8:30 pm in SS-111, the regular classroom.

2. Using Variables • You may declare variables in C. • The declaration includes the data type you need. • Examples of variable declarations: • int meatballs ; • float area ;

3. Declaring Variables • When we declare a variable: • space in memory is set aside to hold that data type • That space is associated with the variable name • Visualization of the declaration • int meatballs ; meatballs FE07

4. Naming Conventions(continued) • Use all uppercase for symbolic constants ( #define ) • Example: PI (#define PI 3.14159 ) • Function names follow the same rules as variables

5. Case Sensitive • C is case sensitive • It matters whether something is upper or lower case • Example: area is different than Area which is different than AREA

6. More Variables • Predefined types in C • Integers • int, long int, short int • Floating point • float, double • Characters • char

7. Keywords in C • int long • register return • short signed • sizeof static • struct switch • typedef union • unsigned void • volatile while • auto break • case char • const continue • default do • double else • enum extern • float for • goto if

8. Which Are Legal Identifiers ? • AREA area_under_the_curve • 3D num45 • Last-Chance #values • x_yt3 pi • num$ %done • lucky***

9. Arithmetic Operators • Name Operator Example • Addition + num1 + num2 • Subtraction - initial - spent • Multiplication * fathoms * 6 • Division / sum / count • Modulus % m % n

10. Modulus % • The expression m % n yields the remainder after m is divided by n. • Modulus is an integer operation. - Both operands MUST be integers. • Examples : 17 % 5 = 2 • 6 % 3 = 0 • 9 % 2 = 1 • 5 % 8 = 5

11. Integer Division • If both operands of a division expression are integers, you get an integer answer. The fractional portion is thrown away. • Examples : 17 / 5 = 3 • 4 / 3 = 1 • 35 / 9 = 3 • Division where one operand is a floating point number will produce a floating point answer. Automatic promotion.

12. Arithmetic Operators Rules of Operator Precedence • Operator(s) Precedence & Associativity • ( ) Evaluated first. If nested - innermost first. If on same level - left to right. • * / % Evaluated second. If many, they are evaluated left to right • + - Evaluated third. If there are several, evaluated left to right. • = Evaluated last, right to left.

13. Relational Operators • < less than • > greater than • < = less than or equal to • > = grater than or equal to • = = is equal to • != is not equal to • Relational expressions evaluate to the int • value 1 (True) or the int value 0 (False) • All of these operators are called binary operators because they take two expressions as operands

14. True or False • Arithmetic expressions also evaluate to true of false. • Any expression that has a zero value is false. ( 0 ) is False • Any expression that has a non-zero value is true. ( 1 ) is True

15. Structured Programming • All programs can be written in terms of only 3 control structures • The sequence structure • Unless otherwise directed, the statements are executed in the order in which they are written. • The selection structure • Used to choose among alternative courses of action • The repetitive structure • Allows that an action is to be repeated while some condition remains true.

16. A Selection Structurethe if statement • if ( condition is “true” ) • { • statement(s) • } • if ( value = = 0 ) • { • printf (“The value you entered was zero\n”); • }

17. Example of if - else • if ( value = = 0 ) • { • printf (“The value you entered was zero\n”); • } • else • { • printf (“You didn’t enter a zero\n”); • }

18. Example • if ( value = = 0 ) • { • printf (“The value you entered was zero\n”); • } • else if ( value < 0 ) • { • printf (“%d is negative.\n”, value); • } • else • { • printf (“%d is positive.\n”, value); • }

19. Gotcha int a = 2; if (a = 1) { printf (“ a is one \n”); } else if (a == 2) { printf (“ a is two \n ”); } else { printf (“ The vaue of a is %d \n”, a); }

20. Our example while loop • children = 10 ; • cookies = 1024 ; • while ( children > 0 ) • { • children = children - 1; • cookies = cookies / 2 ; • }

21. Using a Sentinel Value • We could let the user keep entering the grades and when he’s done enter some special value that signals us that he’s done. • This special signal value is called a sentinel value. • We have to make sure that the value we choose as the sentinel isn’t a legal grade. (ie. can’t use 0 as the sentinel )

22. The Priming Read • When we use a sentinel value to contol a while loop, we have to get the first value from the user before we encounter the loop so that it will be tested and the loop can be entered. • This is known as a priming read. • We have to give significant thought to the initialization of variables, the sentinel value and getting into the loop.

23. Pseudocode for Using a Sentinel to End a while Loop’s Execution • Initialize total to 0 • Initialize counter to 0 • Get the first grade from the user • While the grade != the sentinel value • Add grade to total • Add 1 to counter • Get the next grade (could be sentinel) • average = total / counter • Print the average

24. The cast operator ( ) • We can use a cast operator to create a temporary value of the desired type, to be used in a calculation. • Does NOT change the variable’s type or how it is stored. • Is only good for the statement it’s in. • Often used to avoid integer division. • Used anytime we want to temporarily change a type for a calculation.

25. Using a Sentinel (continued) • while (grade != -1) • { • total = total + grade ; • counter = counter + 1 ; • printf (“Enter grade, -1 to end : “); • scanf (“%d”, &grade); • } • average = ( float ) total / counter ; • printf (“The average was %.2f\n”, average) ; • }

26. Increment and Decrement Operators • The Increment Operator ++ • The Decrement Operator -- • Precedence - lower than (), but higher than * / and % • Associativity - right to left • Increment and decrement operators can only be applied to variables, NOT to constants or expressions

27. Post-Increment Operator • The position of the ++ determines WHEN the value is incremented. If the ++ is after the variable then the incrementing is done last. • int amount, count; • count = 3; • amount = 2 * count++; • amount gets the value of 2 * 3 or 6 and then 1 gets added to count • So after executing the last line, amount is 6 and count is 4.

28. Pre-Increment Operator • If the ++ is before the variable then the incrementing is done first. • int amount, count; • count = 3; • amount = 2 * ++count; • 1 gets added to count first, then amount gets the value of 2 * 4 or 8 • So after executing the last line, amount is 8 and count is 4.

29. Decrement Operator • If we want to subtract one from a variable, we can say: • count = count - 1; • Programs can often contain statements that decrement variables, so to save on typing, C provides these shortcuts : • count- - ; OR - - count; • They do the same thing. Either of these statements change the value of count by subtracting one from it.

30. The for loop Repetitive Structure • The for loop handles details of the counter-controlled loop automatically • The initialization of the the loop control variable, termination conditional test and modification are handled in for loop structure for ( i = 1; i < 11; i++) { initialization modification } test

31. A for loop that countsfrom 0 to 10 for (i = 0; i < 11 ; i++) { printf (“%d”, i); } printf (“\n”);

32. do-while example do { printf (“Enter a positive number: “); scanf (“%d”, &num); if (num < = 0) { printf (“ \n That is not positive, try again \n ”); } } while (num <= 0);

33. for vs while • use a for loop when your program “knows” exactly how many times to loop • use a while loop when there is a condition that will terminate your loop

34. Nested for loops for (i = 1; i < 5; i++) { for (j = 1; j < 3; j+) { if (j % 2 = = 0) { printf (“O”); } else { printf (“X”); } } printf (“\n”); } How many times is the ‘if’ statement executed? What is the output ??

35. The char data type • The char data type holds a single character char ch; • The char is held as a one-byte integer in memory. The ASCII code is what is actually stored, so we can use them as characters or integers, depending on our purpose • Use scanf (“%c”, &ch); to input 1 char

36. Character Example #include <stdio.h> main ( ) { char ch; printf (“Enter a character: “); scanf (“%c”, &ch); printf (“The value of %c is %d.\n”, ch, ch); } If the user entered an A the output would be The value of A is 65.

37. The getchar ( ) function • We can also use the getchar() function that is found in the stdio library • The getchar ( ) function reads one charcter from stdin and returns that character (value) • The value can then be stored in either a char variable or an integer variable

38. getchar () example #include <stdio.h> main ( ) { char grade; printf (“Enter a letter grade: “); grade = getchar ( ); printf (“\nThe grade you entered was %c.\n”, grade); }

39. switch example switch (day) { case 0: printf (“Sunday\n”); break; case 1: printf (“Monday\n”); break; case 2: printf (“Tuesday\n”); break; case 3: printf (“Wednesday\n”); break; case 4: printf (“Thursday\n”); break; case 5: printf (“Friday\n”); break; case 6: printf (“Saturday\n”); break; default: printf (“Error -- unexpected value for day\”); break; }

40. break • The last statement of each ‘case’ in the switch should be (99 % of the time) break; • The break causes program control to jump to the right brace of the switch • Without the break, the code flows into the next case. This is almost never what you want.

41. #define EOF • getchar( ) is usually used to get characters from a file until the “end of file” is reached • The value used to indicate the end of file varies from system to system. It is “system dependent”. • But, regardless of the system we’re using, there is a #define in stdio library for EOF

42. Logical Operators • Logical operators are used for combining condition • && is AND if ( (x > 5) && (y < 6) ) • || is OR if ( (z == 0) || (x > 10) ) • ! is NOT if (! (bob >42) )

43. Example of || if (grade == ‘D’ || grade == ‘F’) { printf (“See you next semester!\n”); }

44. Operator Precedence & Associativity ( ) left to right/inside-out ++ -- ! + (unary) - (unary) (type) right to left * / % left to right + (addition) - (subtraction) left to right < <= > >= left ot right == != left to right && left to right || left to right = += -= *= /= %= right to left , (comma) right to left

45. Examining PrintMessage #include <stdio.h> void PrintMessage (void); function Prototype main ( ) { PrintMessage ( ); function call } void PrintMessage (void) function header { printf (“A message for you:\n\n”); function printf (“Have a Nice Day!\n”); body }

46. Another version ofPrintMessage void PrintMessage (int counter); main ( ) { int num; printf (“Enter an integer: “); scanf (“%d”, &num); PrintMessage (num); one argumentmatches the one } of type intformal parameter of type int void PrintMessage (int counter) { int i; for (i = 0; i < counter; i++) { printf (“Have a nice day\n\n”); } }

47. Using AverageTwo #include <stdio.h> float AverageTwo (int num1, int num2); main ( ) { float average; int num1 = 5, num2 = 8; average = AverageTwo (num1, num2); printf (“The average of %d and %d is %f\n”, num1, num2, average); } float AverageTwo (int num1, int num2) { float average; Promoted to float average = (num1 + num2) / 2.0; return average; }

48. Local Variables • Functions only “see” their own local variable. This includes main ( ) • The variables that are passed to the function are matched with the formal parameters in the order they are passed • The parameters are declarations of local variables. The values passed are assigned to those variables • Other local variables can be declared within the function

49. Data Types andConversion Specifiers Data Type printf scanf conversion conversion float %f %f double %f %lf long double %Lf %Lf int %d %d long int %ld %ld unsigned int %u %u unsigned long int %lu %lu short int %hd %hd char %c %c

50. Commonly Used Header Files header file Contains function prototypes for <stdio.h> the standard input/output library functions & information used by them <math.h> the math library functions <stdlib.h> the conversion of number to text, text to number, memory allocation, random numbers and other utility functions <time.h> maninpulating time and date <ctype.h> functions that test characters for certain properties and that can convert case others see page 159 of text