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. 16, Thursday

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

6. Lexical Elements, Operators, and the C System Lexical Elements, Operators, and the C System • 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?

7. Lexical Elements, Operators, and the C System Introduction • How to check a C program is correct? • 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.

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

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

10. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • Keywords • 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 • Keywords cannot be redefined or used in other contexts.

11. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • Identifiers • What is identifier? • The names of variables, functions, labels and other user-defined items are called identifier. • Special identifier • Keywords, names of functions in C library, main • Rules: • composed of letters, digits, and underscore _ . • The first character must be a letter or underscore. • case-sensitive • would not be defined as the special identifiers:

12. Lexical Elements, Operators, and the C System Lexical Element Lexical Elements • Constants • Integer constants: 0, 17 • Decimal integer: 17 • Octal integer: 017 • Hexadecimal integer: 0x17 • Floating constants: • double, float, long double • Character constants: (enclosed between single quotes)

13. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • String Constants • String constant is a sequence of characters enclosed in a pair of double quote marks. • String constants are differently form character constants. • Special characters: \”, \\ • You mustn't split a string constant across lines • Two string constants that are separated only by white space are concatenated by the compiler into a single string.

14. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • Operators and Punctuator • Precedence and Associativity determine precisely how expressions are evaluated. • Precedence of operators indicates when they will be evaluated. • Associativity • “left to right”: Operations are performed from left to right • Examples: +,-,/,% • “right to left”: Operations are performed from right to left • Examples: ++(prefix), --(prefix)

15. Class on Sept 21

16. 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

17. Lexical Elements, Operators, and the C System Operators and Punctuators— Outline Lexical Elements • Examples of Operators and Punctuators • Precedence and Associativity of Operators • Increment and Decrement Operators • Assignment Operators

18. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Semantics • Precedence and Associativity • Rules

19. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Increment ++i, i++ • Each causes the stored value of i in memory to be incremented by 1. • Each of the expressions ++i and i++ has a value. • ++i • the stored value of i is incremented first • the expression takes as its value the new stored value of i • i++ • the expression takes as its value the current stored value of i • the stored value of i is incremented

20. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements #include <stdio.h> int main(void) { int i, j, a, b; i=0; j=0; a = ++i; b = j++; printf("a=%d, b=%d\n",a,b); return 0; } id.c % gcc id.c % a.out a=1, b=0

21. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • ++ and + • ++ • Cause the value of a variable in memory to be changed • + • Does not change the value of a variable.

22. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Decrement Operator i-- and --i • The value of i is decremented by 1. • Each expression has a value. • --i • the stored value of i is decremented by 1 • the expression takes as its value the new stored valued of i • i-- • the expression takes as its value the current stored valued of i • the stored value of i is decremented by 1

23. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Semantics • Precedence and Associativity • Rules

24. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Precedence and Associativity Associativity • ++ (postfix) -- (postfix) Left to right • +(unary) –(unary) ++(prefix) --(prefix) Right to left • * / % Left to right • + - Left to right

25. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Precedence and Associativity • +(unary) –(unary) ++(prefix) --(prefix) Right to left #include <stdio.h> int main(void) { int a=2; int result; result = - --a; printf("a=2, - --a = %d\n",result); return 0; } Question1: What is the value of a after the operation --a? Question2: What is the value of the expression --a? % gcc id2.c % a.out a=2, - --a = -1 id2.c

26. Lexical Elements, Operators, and the C System ) ) ) ) ( ( ( ( ) ) ( ( Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements ++ a * b – c -- • Examples ++ a * b – 3 #include <stdio.h> int main(void) { int a=1, b=2, c=3, d=4; int result1, result2; result1 = ++ a * b - c --; result2 = 7 - - b * ++ d; printf("++ a * b – c -- = %d\n",result1); printf(“ 7 - - b * ++ d = %d\n",result2); return 0; } id2.c 2 * b – 3 4 – 3 1 • ++ (postfix) -- (postfix) Left to right • +(unary) –(unary) ++(prefix) --(prefix) right to left • * / % left to right • + - left to right • Precedence and Associativity

27. Lexical Elements, Operators, and the C System ) ) ) ( ( ( Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Examples 7 - - b * ++ d #include <stdio.h> int main(void) { int a=1, b=2, c=3, d=4; int result1, result2; result1 = ++ a*b - c --; result2 = 7 - - b * ++ d; printf("++ a * b – c -- = %d\n",result1); printf(“ 7 - - b * ++ d = %d\n",result2); return 0; } id2.c 7 - (-2) * 5 7 - (-10) 17 • ++ (postfix) -- (postfix) Left to right • +(unary) –(unary) ++(prefix) --(prefix) right to left • * / % left to right • + - left to right • Precedence and Associativity

28. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Examples #include <stdio.h> int main(void) { int a=1, b=2, c=3, d=4; int result1, result2; result1 = ++ a*b - c --; result2 = 7 - - b* ++ d; printf("++ a * b – c -- = %d\n",result1); printf(“ 7 - - b* ++ d = %d\n",result2); return 0; } id2.c % gcc id1.c % a.out ++ a * b - c -- = 1 7 - - b* ++ d = 17

29. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Semantics • Precedence and Associativity • Rules

30. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Rules • Applied to variables but not • to constants or • ordinary expressions

31. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Examples: id3.c #include <stdio.h> int main(void) { int a, result1, result2; a = 1; result1 = ++1; result2 = -- -a; return 0; } % gcc id3.c id3.c: In function `main': id3.c:6: error: invalid lvalue in increment id3.c:7: error: invalid lvalue in decrement

32. Lexical Elements, Operators, and the C System Operators and Punctuators— Increment ++ and Decrement Operators -- Lexical Elements • Summary • ++ • ++i: the stored value of i is incremented; the expression takes as its value the new stored valued of i • i++: the expression takes as its value the current stored valued of i; the stored value of i is incremented by 1. • -- • --i: the stored value of i is decremented by 1; the expression takes as its value the new stored valued of i • i--: the expression takes as its value the current stored valued of i; the stored value of i is decremented by 1. • Applied to variables but not to constants or ordinary expression

33. Lexical Elements, Operators, and the C System Operators and Punctuators— Outline Lexical Elements • Examples of Operators and Punctuators • Precedence and Associativity of Operators • Increment and Decrement Operators • Assignment Operators

34. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements • Example: An assignment expression with = • Format: variable = right_side • Two operands • variable • right_side: an expression

35. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements • Example: An assignment expression with = • Format: variable = right_side • Results: • The value of right_side is assigned to variable • Assignment expression variable = right_size has a value. • The value of right_side is the value of the assignment expression. • Example: the value of c is 9 • Assignment expression: a=2+(b=c+1)

36. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements % gcc ass1.c % a.out b = 2, c = 3, a = 5 b1 = 2, c1 = 3, a1 = 5 #include <stdio.h> int main(void) { int a, b, c; int a1, b1, c1; b = 2; c = 3; a = b + c; printf("b = %d, c = %d, a = %d \n",b, c, a); a1=(b1 = 2) + (c1 = 3); printf("b1 = %d, c1 = %d, a1 = %d \n",b1, c1, a1); return 0; }

37. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements • Assignment operators • = • op=: • +=, -=, *=, / =, %=, …… • Semantics: • variable op= expression • equivalent to variable = variable op (expression) • Example: • var*= expr  var=var * expr • a *= 3  a = a * 3

38. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements • Assignment operators • Precedence: • all the assignment operators have the same precedence • Lower than all the other operators which have been introduced (such as + - ) • Associativity: • right to left

39. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements #include <stdio.h> int main(void) { int a, b, c; a = b = c = 0; printf("b = %d, c = %d, a = %d \n", b, c, a); return 0; } % gcc ass2.c % a.out b = 0, c = 0, a = 0

40. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements #include <stdio.h> int main(void) { int i=1, j=2, k=3, m=4; i += j + k; printf(" j = %d, k = %d, i += j+k = %d \n",j, k, i); printf(" m = %d, k = %d, ",m, k); j *= k = m + 5; printf("j *= k = m + 5 = %d \n",j); printf("k = %d \n",k); return 0; } % gcc ass3.c % a.out j = 2, k = 3, i += j+k = 6 m = 4, k = 3, j *= k = m + 5 = 18 k = 9

41. Lexical Elements, Operators, and the C System Operators and Punctuators— Assignment Operators Lexical Elements • Summary • Assignment operators • Precedence: they have the same precedence • Lower than all the other operators which have been introduced (such as + - ) • Associativity: right to left • variable op= expr •  variable = variable op (expr) • The value of the expression is the value of the expr

42. Lexical Elements, Operators, and the C System Operators and Punctuators— Summary Lexical Elements • Precedence and Associativity of Operators • Increment and Decrement Operators • i++, i++ • i--, --i • Assignment Operators • Variable op= expression •  Variable = variable op (expression) • The value of the expression is the value of the expression

43. Lexical Elements, Operators, and the C System Lexical Elements • Summary • Comments • Keywords • Identifiers • Constants • String Constants • Operators and Punctuators

44. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements Comment • 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.

45. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • Keywords • 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 • Keywords cannot be redefined or used in other contexts.

46. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • Identifiers • What is identifier? • The names of variables, functions, labels and other user-defined items are called identifier. • Special identifier • Keywords, names of functions in C library, main • Rules: • composed of letters, digits, and underscore _ . • The first character must be a letter or underscore. • case-sensitive • would not be defined as the special identifiers:

47. Lexical Elements, Operators, and the C System Lexical Element Lexical Elements • Constants • Integer constants: 0, 17 • Decimal integer: 17 • Octal integer: 017 • Hexadecimal integer: 0x17 • An integer may be too large to be stored in a machine word. • Floating constants: double, float, long double • Character constants: (enclosed between single quotes)

48. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • String Constants • String constant is a sequence of characters enclosed in a pair of double quote marks. • String constants are differently form character constants. • Special characters: \”, \\ • You mustn't split a string constant across lines • Two string constants that are separated only by white space are concatenated by the compiler into a single string.

49. Lexical Elements, Operators, and the C System Lexical Elements Lexical Elements • Operators and Punctuators • Precedence and Associativity of Operators • Increment and Decrement Operators • i++, i++ • i--, --i • Assignment Operators • Variable op= expression •  Variable = variable op (expression) • The value of the expression is the value of the expression

50. 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