1. Topic 2 – Introduction to the C Programming Language

2. CISC 105 – Topic 2 What is C? C is a high-level language. A C compiler takes a C source code file as input and produces an executable file, after compiling, assembling, and linking. C is still the industry standard high-level programming language.

3. CISC 105 – Topic 2 An Example C Program /* Converts distances from miles to kilometers */ #include #defineKMS_PER_MILE 1.609 int main(void) { double miles,/* distance in miles */ kms;/* equiv. distance in kms */ /* Get the distance in miles */ printf(“Enter the distance in miles>”); scanf (“%lf”, &miles); /* Convert the distance to kilometers */ kms = KMS_PER_MILE * miles; /* Display the distance in kilometers */ printf (“That equals %f kilometers.\n”,kms); return(0); }

4. CISC 105 – Topic 2 Preprocessor Directives A preprocessor directive is a command given to the C preprocessor, which is a part of the compilation process that modifies a C source code file before it is compiled. Preprocessor directives always begin with a “#” character. In the example program, there are two preprocessor directives used, #include and #define.

5. CISC 105 – Topic 2 #include The #include directive tells the C preprocessor to give a program access to a library. By putting a #include in a program, the preprocessor loads a header file, which tells the compiler what functions and other information is provided in the library. In this program, #include indicates that this program uses the stdio library which contains functions such as printf().

6. CISC 105 – Topic 2 #define The #define directive specifies a constant macro. This tells the preprocessor that every time it encounters the first text, it should replace it with the second text. In this program, #define KMS_PER_MILE 1.609 tells the preprocessor to replace KMS_PER_MILE with 1.609 every place KMS_PER_MILE appears in the program.

7. CISC 105 – Topic 2 Preprocessor Directives /* Converts distances from miles to kilometers */ #include #defineKMS_PER_MILE 1.609 int main(void) { double miles,/* distance in miles */ kms;/* equiv. distance in kms */ /* Get the distance in miles */ printf(“Enter the distance in miles>”); scanf (“%lf”, &miles); /* Convert the distance to kilometers */ kms = KMS_PER_MILE * miles; /* Display the distance in kilometers */ printf (“That equals %f kilometers.\n”,kms); return(0); } #include directive – Tells the preprocessor to include the stdio.h header file. This file describes the functions and other information included in the stdio library. #define directive – Tells the preprocessor to replace every occurrence of KMS_PER_MILE in the program with 1.609.

8. CISC 105 – Topic 2 Comments Comments are text provided by the programmer to allow others (and the programmer too) to better understand what the program is doing Any text between a “/*” and a “*/” is considered to be a comment and is ignored by the C preprocessor and the compiler itself. Comments can appear anywhere in a program and can be multiline.

9. CISC 105 – Topic 2 Comments /* Converts distances from miles to kilometers */ #include #defineKMS_PER_MILE 1.609 int main(void) { double miles,/* distance in miles */ kms;/* equiv. distance in kms */ /* Get the distance in miles */ printf(“Enter the distance in miles>”); scanf (“%lf”, &miles); /* Convert the distance to kilometers */ kms = KMS_PER_MILE * miles; /* Display the distance in kilometers */ printf (“That equals %f kilometers.\n”,kms); return(0); } comment – Ignored by the C preprocessor and the compiler.

10. CISC 105 – Topic 2 Reserved Words Reserved words are words the have special meaning in the C language and cannot be used for other purposes. In this program, examples include int, void, double, and return.

11. CISC 105 – Topic 2 Reserved Words /* Converts distances from miles to kilometers */ #include #defineKMS_PER_MILE 1.609 int main(void) { double miles,/* distance in miles */ kms;/* equiv. distance in kms */ /* Get the distance in miles */ printf(“Enter the distance in miles>”); scanf (“%lf”, &miles); /* Convert the distance to kilometers */ kms = KMS_PER_MILE * miles; /* Display the distance in kilometers */ printf (“That equals %f kilometers.\n”,kms); return(0); } Reserved Words – These have special meaning in C and cannot be used for anything else.

12. CISC 105 – Topic 2 Identifiers Identifiers identify memory cells that hold data or operations (and functions). Standard identifiers have special meaning in C, however they can be redefined by the programmer. Examples of standard identifiers in the program are printf and scanf. User-defined identifiers memory cells that hold data, operations, and functions that the programmer defines.

13. CISC 105 – Topic 2 Identifiers /* Converts distances from miles to kilometers */ #include #defineKMS_PER_MILE 1.609 int main(void) { double miles,/* distance in miles */ kms;/* equiv. distance in kms */ /* Get the distance in miles */ printf(“Enter the distance in miles>”); scanf (“%lf”, &miles); /* Convert the distance to kilometers */ kms = KMS_PER_MILE * miles; /* Display the distance in kilometers */ printf (“That equals %f kilometers.\n”,kms); return(0); } Standard Identifiers User-defined Identifiers

14. CISC 105 – Topic 2 What is a valid identifier? Identifiers can only be composed of letters, digits, and underscores. Identifiers cannot begin with a digit. Reserved words cannot be identifiers. Identifiers can be as long as you want. Upper and lower case letters are different (i.e. kms and Kms are not considered to be the same identifier).

15. CISC 105 – Topic 2 Review Which of the following are valid identifiers? For each that is not valid, why is it not? This_is_a_long_identifier_but_is_it_valid? 8timesTheRadius miles Jeff’s variable kilometers_per_hour “radius” x

16. CISC 105 – Topic 2 Variables A variable is a memory cell that is used to hold data acted upon by the program. A variable declaration tells the C compiler the name and type of a variable used in a program. A variable declaration consists of a data type and an identifier which is the name of that variable. Every variable that will be used in a program must be declared.

17. CISC 105 – Topic 2 Variable Declarations The first line declares a variable named mile of the double data type. The second line declares a a variable named counter of the int data type. doublemile; intcounter;

18. CISC 105 – Topic 2 Data Types There are a large number of data types. These are some of the most popular ones. void – this keyword means “no data type”. int – An integer (a whole number). This data type can represent an integer in a specific range, at least –32767 through 32767.

19. CISC 105 – Topic 2 Data Types char – A character. One letter, digit, or symbol This is enclosed in single quotes. float – A real number (an integer part and a decimal part). double – A real number. Note that this data type is a memory cell double the size of a float data type. This allows a bigger number to be represented, or a specific number to be represented more precisely. This is referred to a a double-precision floating point number.

20. CISC 105 – Topic 2 Bigger or More Precise? Why can be represent either bigger numbers or more precise numbers? Because floating points numbers are stored in scientific notation, consisting of a number and an exponent, i.e. 1.2555 x 10^6

21. CISC 105 – Topic 2 Review of Variables Write a #define preprocessor declaration for a constant macro of STUDENTS_PER_SECTION to 22 and variable declarations of num_students as an integer, GPA and class_GPA as double-precision floating point numbers, and letter_grade as a character data type. #define STUDENTS_PER_SECTION 22 int num_students; double GPA, class_GPA; char letter_grade;

22. CISC 105 – Topic 2 Assignment Statements An assignment statement is one type of executable statement. An assignment statement uses the “=“ operator, and follows the form: variable = expression; This statement first evaluates the expression on the right and stores the result in the variable on the left.

23. CISC 105 – Topic 2 Assignment Statements Here are some examples of assignment statements: x = 12; negative_x = -x; x = y + 12 + z * 5; result = y; Note that any variables in the right-side expression are not modified by an assignment statement.

24. CISC 105 – Topic 2 Function Calls A function is a piece of code which performs a specific task. Functions can be created by programmers or supplied as part of the C compiler toolset. A function is called, which causes it to execute. A function is composed of the function name, an open paren, a set of function arguments separated by commas, and a close paren.

25. CISC 105 – Topic 2 Function Calls A function call looks like this: function_name(argument1, argument2, argument3); function namefunction arguments open paren close paren

26. CISC 105 – Topic 2 The printf Function The C function for displaying output on the screen to the user is printf. printf is called in the following manner: printf(“The final GPA of student number %d is %f.\n”,student_num, GPA); format stringprint listfunction arguments

27. CISC 105 – Topic 2 The Format String and Print List The format string is the text that is to be displayed on the screen. The “%” characters are called placeholders. They indicate the display position for variables whose values are to be displayed. The variable names to be displayed are specified in the print list and appear in the same order as their placeholders.

28. CISC 105 – Topic 2 Placeholders printf(“The final GPA of student number %d is %f.\n”,student_num, GPA); This pair specifies the location in the print string to display the student_num value. This pair specifies the location in the print string to display the GPA value.

29. CISC 105 – Topic 2 Placeholders All placeholders begin with a “%”. The text after the “%” symbol indicate how to format the output, i.e. what kind of variable it is. %d – decimal number ( int ) %f – floating-point number ( float or double ) %c – character ( char )

30. CISC 105 – Topic 2 Escape Sequences All escape-sequences begin with a “\”. In order to display a “\”, the format string must contain a “\\”. A letter after the “\” character denotes an escape sequence, which has special meaning. The “\n” sequence indicates a new-line character, which cause any following text to appear on the next line on the display.

31. CISC 105 – Topic 2 Placeholders and the Newline Escape Sequence printf(“The final GPA of student number %d is %f.\n”,student_num, GPA); Specifies to display student_num, which is an integer. Specifies to display GPA, which is an floating-point number. Therefore, if the student_num variable was set to 10 and the GPA variable was set to 3.03 this printf function call would cause The final GPA of student number 10 is 3.03. to be displayed on the screen and any subsequent output to begin on the next line.

32. CISC 105 – Topic 2 The scanf Function The C function for reading input from the user is scanf. scanf(“%d %f”,&student_num, &GPA); format stringinput listfunction arguments

33. CISC 105 – Topic 2 The Format String The format string is the set of placeholders which specify what type of data is being input. The same placeholders are used as for printf, except for when inputting a floating-point number. A float type still uses the “%f”, however the double type uses the “%lf” placeholder.

34. CISC 105 – Topic 2 The Input List The variables to store the inputted data are specified in the input list. They must be in the same order as their corresponding placeholders. Notice that each variable name is preceded by a “&”. The “&” is an operator which means “the address of”. Therefore, “&student_num” tells the scanf function to store what it reads from the user at the memory address of student_num.

35. CISC 105 – Topic 2 Placeholders and the Input List scanf(“%d %f”,&student_num, &GPA); This pair specifies to read in a integer and store it at the memory address of student_num, thus setting the student_num variable to the inputted value. This pair specifies to read in a single-precision floating point number and store it at the memory address of GPA, thus setting the GPA variable to the inputted value. Therefore, if the input into this scanf function call was: 9 3.560 the student_num variable would be set to 9 and the GPA variable would be set to 3.560

36. CISC 105 – Topic 2 Review of printf and scanf What happens when the following code fragment is run? int student_num; float GPA; printf(“Enter the student number>”); scanf(“%d”,&student_num); printf(“Enter student number %d’s GPA>”,student_num); scanf(“%f”,&GPA); printf(“Student number %d now has a %f GPA.\n”,student_num, GPA);

37. CISC 105 – Topic 2 Review of printf and scanf What is the displayed output when the following code fragment is run and the input are 8 and 12? int x, y; printf(“My name is”); printf(“ Jeffrey A. Six.”); printf(“\nEnter two integers> ”); scanf(“%d%d”,&x, &y); x = x + 2; y = x + y; printf(“Thanks! The answer is %d.\nBye now!”,y); My name is Jeffrey A. Six. Enter two integers> 8 12 Thanks! The answer is 22. Bye now!

38. CISC 105 – Topic 2 Customizing Integer Output The “%d” placeholder, used to display an integer variable, can be altered to format how the number is displayed. Instead of “%d”, use a “%Xd” where the X is an integer that is the field width, the number of digits to display. For example, “%4d” displays four digits of the result. The negative sign (for negative integers) is also considered a digit here.

39. CISC 105 – Topic 2 Customizing Integer Output When there are more places (the field width) than digits to be displayed, the output is right-justified. When there are more digits than places, the output is field width is ignored, and the entire integer is displayed.

40. CISC 105 – Topic 2 Customizing Integer Output As an example: ValuePlaceholderOutput 643%1d643 %4d 643 %5d 643 -643%2d-643 %6d -643

41. CISC 105 – Topic 2 Customizing Floating-Point Output Floating point output ( float and double ) can be formatted in the same manner, using “%X.Yf”). Here, X is the total number of digits to display (the field width) and Y is the number of digits to display to the right of the decimal point. The same rules for field width apply as for integer formatting. The specified number of decimal digits is always displayed.

42. CISC 105 – Topic 2 Customizing Floating-Point Output ValuePlaceholderOutput 3.14159%5.2f 3.14 3.14159%3.2f3.14 3.14159%5.3f3.142 0.1234%4.2f0.12 -0.006%8.5f-0.00600 As an example:

43. CISC 105 – Topic 2 The return Function The return function terminates a running function and returns control to the function that called the function. In the case of main(), the return function returns control back to the computer’s operating system and ends the program. This function has one argument. The main() function must return an integer, normally just set to 0 (zero).

44. CISC 105 – Topic 2 Arithmetic Expressions Arithmetic expressions are executable statements that manipulate data. Arithmetic expressions operate on both integer ( int ) and floating-point ( float and double ) numbers. Arithmetic operators can operate on mixed types (i.e. one int and one float ). The resulting type of such an expression is the “highest” data type present.

45. CISC 105 – Topic 2 Resulting Data Types The “highest” data type is always considered to be a floating point number, with double-precision floating point numbers taking precedence over single-precision floating point numbers. int + int = int int + float = float int + double = double float + double = double

46. CISC 105 – Topic 2 Arithmetic Expressions All of the common arithmetic operators are present in C: +(addition) - (subtraction) *(multiplication) /(division) %(modulus – or “remainder”)

47. CISC 105 – Topic 2 Note: Integer Division If two integer values are divided, the resulting data type is also an integer, as previously described. Therefore, only the integer portion of the actual result will be the returned result. For example, 9 / 4 = 2 9 / 10 = 0

48. CISC 105 – Topic 2 The Modulus Operator The “%” operator is a modulus operator, which also means the remainder of the division. For example, 9 % 3= 0 10 % 6= 4 90 % 8= 2

49. CISC 105 – Topic 2 Review of Basic Arithmetic Expressions What is the resulting output of this program segment? int x, y, z; float a; x = 9 * 0.5; a = 9 * 0.5; y = 15 % 15; z = 15 % 2; printf(“x=%d, a=%f, y=%d, z=%d\n”,x,a,y,z) x=4, a=4.5, y=0, z=1

50. CISC 105 – Topic 2 More Complex Arithmetic Expressions C evaluates arithmetic expressions in the same order rules as normal mathematics. Parentheses take priority over everything else. Then, multiplication, division, and modulus operations from left to right. Then, addition and subtraction from left to right.

51. CISC 105 – Topic 2 More Complex Arithmetic Expressions x 2 + 2xy + 4y 2 (x * x) + (2 * x * y) + (4 * y * y) a + b -------- c 2 * 4d (a + b) / (c * c * 4 * d) a * (4x % y 2 ) a * (4 * x % (y * y)) x + y(x 2 + y) x + y * (x * x + y)

52. CISC 105 – Topic 2 Review #definePI 3.14159 int x, y, z; float a, b; x = 5; y = 10; z = x + (4 * y * y * y) + PI; a = x + (4 * y * y * y) + PI; b = (x / y) + a; printf(“x=%d, y=%d, z=%d\na=%7.2f, b=%f\n”,x,y,z,a,b); What is the resulting output of this program segment? x=5, y=10, z=4008 a=4008.14, b=4008.14159

53. CISC 105 – Topic 2 Special Case: Operations on a Variable Often, one wishes to perform an operation on a variable, such as adding or subtracting a value. C has a special syntax for an operation performed on a variable (i.e. the variable is used on the right side of the assignment statement and is the target of the assignment as well.)

54. CISC 105 – Topic 2 Special Case: Operations on a Variable This syntax follows the form: variable (operation)= expression; This statement first computes the operation on the right side of the equals sign. Then, it performs the (operation) on the variable and the expression.

55. CISC 105 – Topic 2 Special Case: Operations on a Variable For example, This statement adds 19 to the value contained in x. This statement is exactly the same as x += 19; x = x + 19;

56. CISC 105 – Topic 2 Another Special Case: Increment and Decrement Incrementing (adding one) and decrementing (subtracting one) are two very common operations. C has a special syntax for increment and decrement operations that follows this form: x++;++x;--x;x--;OR IncrementDecrement

57. CISC 105 – Topic 2 Another Special Case: Increment and Decrement Notice that the increment operator expression x++ is the same as saying: x += 1; So, why are there two forms of each operator? The answer lies in when the increment (or decrement) operation is actually performed. This distinct only occurs when the ++ (or --) operator is used on a variable in the same expression in which the value of the variable is used.

58. CISC 105 – Topic 2 Another Special Case: Increment and Decrement For example, int x = 20, y; y = x++; printf(“x=%d, y=%d\n”,x,y); int x = 20, y; y = ++x; printf(“x=%d, y=%d\n”,x,y); x=21, y=20x=21, y=21 y = x; x += 1; printf(“x=%d, y=%d\n”,x,y); x += 1; y = x; printf(“x=%d, y=%d\n”,x,y);

59. CISC 105 – Topic 2 Another Special Case: Increment and Decrement The difference lies in when the expression (x++ or ++x) gets evaluated in relation to when the operator (++) gets performed. The x++ expression is equal to the value of x and the ++ operator is performed after the evaluation is over. The ++x expression indicates that the ++ operator is performed first (before ++x is evaluated) and thus, is equal to the value of x + 1.

60. CISC 105 – Topic 2 Review What is the output of the following program fragment? int x, y, z; x = 5; y = 10; z = x++ * y – 2; z += ++x; printf(“x=%d, y=%d, z=%d\n”,x,y,z); x=7, y=10, z=55