Welcome to CPSC 206

1. Welcome to CPSC 206 Structured Programming in C

2. Lecture Information http://people.cs.tamu.edu/ychen/Teaching/CPSC206

3. 0. Introduction to Computer Science 1. Overview of C Ch 1, 2 Lecture Topics: Features of C: 2. Flow of control and functions Ch 3, 4 3. Character processing & fundamental data types Ch 5, 6 4. File I/O Ch 13 5. Pointers, Arrays, and Strings Ch 8, 9, 10 6. Structures, and linked lists Ch 12 7. Enumeration type and storage classes Ch 7, 8 8. Recursion Ch 11

4. Review of Class on Sept. 14, Tuesday

5. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations.

6. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. The general form of a program preprocessing directives int main () { declarations statements }

7. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. • Declarations • Purpose: Tell the compiler what kind of data can be stored in each of the variables. • The compiler can set aside the appropriate amount of memory to hold the data. • Format: • Data_Type Variable1, Variable2;

8. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. • Variables • A variable name can be a sequence of letters, digits, and underscores. • A variable name may not begin with a digit. • Certain keywords, also called reserved words, cannot be used as names of variables.

9. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. • Expressions • How to use expressions? • on the right side of assignment • Arguments to functions • How to construct an expression? • Constants • The name of a variable • Meaningful combinations of operators with variables and constants

10. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. • Integer: • Division a/b: an integer expression divided by another integer expression yields an integer value. • Any fractional part is discarded. • Modulus a%b: the remainder after a is divided by b. • If a or b is negative, the results of division and modulus are system-dependent • In a/b and a%b, the value of b cannot be zero.

11. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. • Character: • Constants are written within single quotes • Example: • ‘A’ ‘1’

12. A Depth Program: Algorithm and code • Dissection of the depth program Declaration main Function printf function • Basics of C Programming General form of a program Declaration Variable Expression Data Type and Operation An Overview of C— Chapter 1 • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. • Floating types: • float: an F suffix • 1.22F • double: unsuffixed floating constant • 1.22 • long double: an L suffix • 1.22L

13. Initialization • A variable can be initialized when it is declared. • Constants or constant expressions can be used to initialize a variable. • Declared variables can be used to initialize a variable. • a variable cannot be used before it has been declared. • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. An Overview of C— Outline

14. Preprocessing directives: • #include “filename” • The preprocessor replaces the line with a copy of the named file. • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. An Overview of C— Outline

15. Preprocessing directives: • #define A B • It affects only those lines in the file that come after it. • All occurrences (after this line)of the identifier A, except in quoted string, will be changed to B. • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. An Overview of C— Outline

16. Print and Read formatted data • Arguments: control_string and other_arguments • control_string contains formats, called conversion specifications, which are matched with other arguments. • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. An Overview of C— Outline

17. Print and Read formatted data • How to specify format using conversion specification? • %field_widthconversion_character • %field_width.precisionconversion_character • conversion_character: how the data is printed? • c: as a character • d: as a decimal integer • f: as a floating-point number • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. An Overview of C— Outline

18. Print and Read formatted data • Example: scanf(“%d”, &x); &: address operator • %d — how to interprete the input stream • the input characters typed at the keyboard is interpreted as a decimal integer • &x — where to store the value • the value of the decimal integer is stored at the address of x. • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. An Overview of C— Outline

19. The while statement while (expression) statement statement is executed as long as the value of expression is true • A brief history of C • Features of C • Get Ready to Program • A First Program • The Basics of C Programming • Variables, Expressions, and Assignments • Initialization • Preprocessing directives: #define and #include • Print and Read formatted data: printf() and scanf() • The while statement • Problem Solving: Computing Sums • Style, Programming Errors and System Considerations. An Overview of C— Outline

20. Review of Class on Sept. 14, Tuesday End

21. Chapter 2:Lexical Elements, Operators, and the C System

22. Lexical Elements, Operators, and the C System Introduction • C is a language. •  C has an alphabet •  C has rules for putting together words and punctuation to make legal programs.

23. Lexical Elements, Operators, and the C System Introduction • C is a language. • C has an alphabet • Lowercase letters: a b c …… z • Uppercase letters: A B C …… Z • Digits: 0 1 2 3 4 5 6 7 8 9 • Other characters: • + - * / = ( ) { } [ ] < > ‘ “ ! @ # $ % & _ | ^ ~ \ . , ; : ? • White space characters: • blank, newline, tab, etc.

24. Lexical Elements, Operators, and the C System Introduction • C is a language. • C has rules for putting together words and punctuation to make legal programs. • These rules are called syntax

25. Lexical Elements, Operators, and the C System Introduction • C is a language • Alphabet • syntax • What is C program? • A C program is a sequence of characters How a computer understands this sequence of characters?

26. Lexical Elements, Operators, and the C System Introduction Machine code object code C code Preprocessor Compiler Loader errors How does a compiler know whether a C program is correct or not?

27. Lexical Elements, Operators, and the C System Introduction • How to check a C program is correct? • Compiler • The program that checks the legality of a program. • How compiler checks the legality of a program? • The characters are collected by the compiler into syntactic units called tokens • The compiler checks whether the tokens can be formed into legal strings according to the syntax of C language.

28. Lexical Elements, Operators, and the C System Introduction • In C language, there are six kinds of tokens: • Keywords • Identifiers • Constants • String constants • Operators • Punctuators

29. Lexical Elements, Operators, and the C System Outline • An Example — Characters and Lexical Elements • Lexical Elements • Comments • Keywords • Identifiers • Constants • String Constants • Operators and Punctuators • An Example: Computing Powers of 2 • The C System

30. Lexical Elements, Operators, and the C System Comment: be replaced with a single blank An Example — Characters and Lexical Elements sum.c /* Read in two scores and print their sum. */ #include <stdio.h> int main(void) { int score_1, score_2, sum; printf("Input two scores as integers: "); scanf("%d%d", &score_1, &score_2); sum = score_1 + score_2; printf("%d + %d = %d\n", score_1, score_2, sum); return 0; }

31. Lexical Elements, Operators, and the C System File stdio.h is included An Example — Characters and Lexical Elements sum.c #include <stdio.h> int main(void) { int score_1, score_2, sum; printf("Input two scores as integers: "); scanf("%d%d", &score_1, &score_2); sum = score_1 + score_2; printf("%d + %d = %d\n", score_1, score_2, sum); return 0; }

32. Lexical Elements, Operators, and the C System An Example — Characters and Lexical Elements sum.c int main(void) { int score_1, score_2, sum; printf("Input two scores as integers: "); scanf("%d%d", &score_1, &score_2); sum = score_1 + score_2; printf("%d + %d = %d\n", score_1, score_2, sum); return 0; } • Keyword: • int • void • Identifier: • main • score_1 • score_2 • sum • Operator: • Parentheses ( ) • Punctuators: • ; • , • { A Copy of stdio.h

33. Lexical Elements, Operators, and the C System An Example — Character and Lexical Elements int main(void) { int score_1, score_2, sum; • How the compiler distinguishs tokens? • white space • For example: int score_1s • What if we write as follows? • intscore_1, score_2, sum; • The compiler considers intscore_1 as a single token.

34. Lexical Elements, Operators, and the C System An Example — Characters and Lexical Elements % gcc sum1.c sum1.c: In function `main': sum1.c:8: error: `intscore_1' undeclared (first use in this function) sum1.c:8: error: (Each undeclared identifier is reported only once sum1.c:8: error: for each function it appears in.) sum1.c:8: error: `score_2' undeclared (first use in this function) sum1.c:8: error: `sum' undeclared (first use in this function) sum1.c:11: error: `score_1' undeclared (first use in this function) sum1.c /* Read in two scores and print their sum. */ #include <stdio.h> int main(void) { intscore_1, score_2, sum; printf("Input two scores as integers: "); scanf("%d%d", &score_1, &score_2); sum = score_1 + score_2; printf("%d + %d = %d\n", score_1, score_2, sum); return 0; }

35. Lexical Elements, Operators, and the C System An Example — Characters and Lexical Elements • Identifier: • printf • scanf • Operator: • ( • ) • & • Punctuators: • , • ; • String Constant • A series of characters enclosed in “ ” sum.c int main(void) { int score_1, score_2, sum; printf("Input two scores as integers: "); scanf("%d%d", &score_1, &score_2); sum = score_1 + score_2; printf("%d + %d = %d\n", score_1, score_2, sum); return 0; } A Copy of stdio.h

36. Lexical Elements, Operators, and the C System An Example — Characters and Lexical Elements • Identifier: • sum • score_1 • score_2 • Operator: • + • = • Punctuators: • ; • Constant • 0 sum.c int main(void) { int score_1, score_2, sum; printf("Input two scores as integers: "); scanf("%d%d", &score_1, &score_2); sum = score_1 + score_2; printf("%d + %d = %d\n", score_1, score_2, sum); return 0; } A Copy of stdio.h

37. Lexical Elements, Operators, and the C System An Example — Characters and lexical Elements • Summary • Tokens: • Keyword: int void • Identifier:printf scanf sum • Operator: ( ) & • Punctuators: ;} • Constant: 0 • String Constant: “Input two scores as integers: “ • Separate two tokens: white space

38. Lexical Elements, Operators, and the C System Outline • An Example — Characters and Lexical Elements • Lexical Elements • Comments • Keywords • Identifiers • Constants • String Constants • Operators and Punctuators • An Example: Computing Powers of 2 • The C System

39. Lexical Elements, Operators, and the C System Comments Lexical Elements • What is comment? • Arbitrary strings of symbols placed between the delimiters /* and */. • Single line comment: // text • How compiler processes comments? • The compiler changes each comment into a single blank character. • Why comment? • Comments are used by the programmer as a documentation aid.

40. Lexical Elements, Operators, and the C System Comments Lexical Elements • Rule1: Where can we place comments? • Anywhere? • No • Compiler replaces each comment by a single blank character  • Comments can be placed wherever a single blank character can appear. • Example x = 10+/* add the numbers */5;  x = 10+ 5;

41. Lexical Elements, Operators, and the C System Comments Lexical Elements comment.c #include <stdio.h> int main(void) { int/* a comment*/x; x=10+5; printf("x=%d\n",x); return 0; } % gcc comment.c % a.out x=15 int x;

42. Lexical Elements, Operators, and the C System Comments Lexical Elements • Question: Can a comment appear in the middle of a keyword or identifier? • Compiler will insert a single blank character into a keyword or identifier • Since a blank is used to separate two tokens, the keyword or identifier will be considered as two tokens. •  No

43. Lexical Elements, Operators, and the C System int x, x y; Comments Lexical Elements #include <stdio.h> int main(void) { int x, x/* a comment */y; return 0; } comment1.c % gcc comment1.c comment1.c: In function `main': comment1.c:6: error: redeclaration of `x' comment1.c:6: error: `x' previously declared here comment1.c:6: error: parse error before "y"

44. Lexical Elements, Operators, and the C System Comments Lexical Elements • Rule2: nested comments • Multi-Line comments may not be nested. Example: /* outer comment /* inner comment */ */ • A single-line (//) comment can be nested within a multi-line comment. Example: /* a //test of nested comments. */

45. Lexical Elements, Operators, and the C System */ Comments Lexical Elements • An understanding of Rule2: Usually when a compiler encounters a pair /*, • it considers text between this /* and the first occurrence of */ after this /* as a comment; • this comment is replaced by a blank character. • /* outer comment /* inner comment */ */ • /* a //test of nested comments */

46. Lexical Elements, Operators, and the C System Comments Lexical Elements #include <stdio.h> int main(void) { int x=1; /* This is a comment /* */ return x; } #include <stdio.h> int main(void) { int x; /* //*/ return 0; } comment3.c comment2.c

47. Lexical Elements, Operators, and the C System Comment Lexical Elements Summary • What is comment? • Arbitrary strings of symbols placed between the delimiters /* and */. • Single line comment: // text • The compiler changes each comment into a single black character. • Rules: • Multi-line comments cannot be placed in the middle of a keyword or identifier. • Multi-line comments may not be nested.

48. Lexical Elements, Operators, and the C System Outline Lexical Elements • An Example — Characters and Lexical Elements • Lexical Elements • Comments • Keywords • Identifiers • Constants • String Constants • Operators and Punctuators • An Example: Computing Powers of 2 • The C System

49. Lexical Elements, Operators, and the C System Keywords Lexical Elements • What is Keywords? • Keywords are explicitly reserved words that have a strict meaning as individual tokens in C. • Examples of Keywords • Data Type: int, char, long, short C is small Compared to other major languages, C has only a small number of keywords.

50. Lexical Elements, Operators, and the C System Keywords Lexical Elements • Rules: • Keywords cannot be redefined or used in other contexts. • Example: • keywords cannot be used as variable names.