C the basic concepts


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C the basic concepts

  1. 1. B E GINNING WITH THE C The Stack OverflowDennis M. Ritchie
  2. 2. INTRODUCTION• C programming language – Structured and disciplined approach to program design. C is developed by Dennis Ritchie C is a structured programming language C supports functions that enables easy maintainability of code, by breaking large file into smaller modules Comments in C provides easy readability C is a powerful language. C programs built from  Variable and type declarations  Functions  Statements  Expressions
  3. 3. PROGRAM STRUCTUREA sample C Program#include<stdio.h>int main(){ --other statements}
  4. 4. HEADER FILES The files that are specified in the include section is called as header file These are precompiled files that has some functions defined in them We can call those functions in our program by supplying parameters Header file is given an extension .h C Source file is given an extension .c
  5. 5. MAIN FUNCTION This is the entry point of a program When a file is executed, the start point is the main function From main function the flow goes as per the programmers choice. There may or may not be other functions written by user in a program Main function is compulsory for any C program
  6. 6. RUNNING A ‘C’ PROGRAM Type a program Save it Compile the program – This will generate an exe file (executable) Run the program (Actually the exe created out of compilation will run and not the .c file) In different compiler we have different option for compiling and running. We give only the concepts.
  7. 7. C LANGUAGE TOKENSWhat are actually tokens? The smallest individual units in a C program are known as tokens. In a C source program, the basic element recognized by the compiler is the "token." A token is source-program text that the compiler does not break down into component elements.
  8. 8. TOKEN TYPES IN ‘C’ C has 6 different types of tokens viz.2.Keywords [e.g. float, int, while]3.Identifiers [e.g. main, amount]4.Constants [e.g. -25.6, 100]5.Strings [e.g. “SMIT”, “year”]6.Special Symbols [e.g. {, }, [, ] ]7.Operators [e.g. +, -, *]C programs are written using these tokens and the general syntax.
  9. 9. THE KEYWORDS "Keywords" are words that have special meaning to the C compiler. Their meaning cannot be changed at any instance. Serve as basic building blocks for program statements. All keywords are written in only lowercase.
  10. 10. KEYWORDS IN ANSI Cauto double register switchbreak else return typedefcase enum short unionchar etern signed unsignedconst float sizeof voidcontinue for static volatiledefault goto struct whiledo if int long
  11. 11. THE IDENTIFIERS They are programmer-chosen names to represent parts of the program: variables, functions, etc. Cannot use C keywords as identifiers Must begin with alpha character or _, followed by alpha, numeric, or _ Upper- and lower-case characters are important (case-sensitive) Must consist of only letters, digits or underscore ( _ ). Only first 31 characters are significant. Must NOT contain spaces ( ).
  13. 13. ABOUT CONSTANTS Constants in C are the fixed values that do not change during the execution of a program. CONSTANTS Numeric constants Character constants Real Single Integer String Constants Character Constants Constants Constants
  14. 14. CONSTANTS EXAMPLES Integer Constants  Refers to sequence of digits such as decimal integer, octal integer and hexadecimal integer.  Some of the examples are 112, 0551, 56579u, 0X2 etc. Real Constants  The floating point constants such as 0.0083, -0.78, +67.89 etc. Single Character Constants  A single char const contains a single character enclosed within pair of single quotes [ ‘ ’ ]. For example, ‘8’, ‘a’ , ‘i’ etc. String Constants  A string constant is a sequence of characters enclosed in double quotes [ “ ” ]; For example, “0211”, “Stack Overflow” etc.
  15. 15. DECLARATIONS Constants and variables must be declared before they can be used. A constant declaration specifies the type, the name and the value of the constant. any attempt to alter the value of a variable defined as constant results in an error message by the compiler A variable declaration specifies the type, the name and possibly the initial value of the variable. When you declare a constant or a variable, the compiler: 1. Reserves a memory location in which to store the value of the constant or variable. 2. Associates the name of the constant or variable with the memory location.
  16. 16. WHAT ARE VARIABLES IN C? A Variable is a data name that is used to store any data value. Variables are used to store values that can be changed during the program execution. Variables in C have the same meaning as variables in algebra. That is, they represent some unknown, or variable, value. x=a+b z + 2 = 3(y - 5) Remember that variables in algebra are represented by a single alphabetic character.
  17. 17. NAMING VARIABLES Variables in C may be given representations containing multiple characters. But there are rules for these representations. Variable names in C  May only consist of letters, digits, and underscores  May be as long as you like, but only the first 31 characters are significant  May not begin with a number  May not be a C reserved word (keyword)  Should start with a letter or an underscore(_)  Can contain letters, numbers or underscore.  No other special characters are allowed including space.
  18. 18. NAMING CONVENTIONS C programmers generally agree on the following conventions for naming variables.  Begin variable names with lowercase letters  Use meaningful identifiers  Separate “words” within identifiers with underscores or mixed upper and lower case.  Examples: surfaceArea surface_Area surface_area  Be consistent while naming the variables! Use all uppercase for symbolic constants (used in #define preprocessor directives). Examples: #define PI 3.14159 #define AGE 52
  19. 19. CASE SENSITIVITY C is a case sensitive language.  It matters whether an identifier, such as a variable name, is uppercase or lowercase.  Example: area Area AREA ArEa are all seen as different variables by the compiler.
  20. 20. DECLARING VARIABLES Before using a variable, you must give the compiler some information about the variable; i.e., you must declare it. The declaration statement includes the data type of the variable. Examples of variable declarations: int length ; float area ;
  21. 21. DECLARATION (CONTD.) Variables are not automatically initialized. For example, after declaration int sum; the value of the variable sum can be anything (garbage). Thus, it is good practice to initialize variables when they are declared. Once a value has been placed in a variable it stays there until the program alters it.
  22. 22. DATA TYPES IN ‘ANSI C’ There are three classes of data types here:: Primitive data types  int, float, double, char Aggregate OR derived data types  Arrays come under this category  Arrays can contain collection of int or float or char or double data User defined data types  Structures and enum fall under this category.
  23. 23. DATA TYPES- DIFFERENT ATTRIBUTESType Size Representation Minimum range Maximum rangechar, signed char 8 bits ASCII -128 127unsigned char bool 8 bits ASCII 0 255short, signed short 16 bits 2s complement -32768 32767unsigned short 16 bits Binary 0 65535int, signed int 16 bits 2s complement -32768 32767unsigned int 16 bits Binary 0 65535long, signed long 32 bits 2s complement -2,147,483,648 2,147,483,647unsigned long 32 bits Binary 0 4,294,967,295float 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38double 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38long double 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38
  24. 24. DATA TYPES : 1- INTEGER An integer type is a number without a fractional part. Represents a signed integer of typically 4 or 8 bytes (32 or 64 bits). Precise size is machine-dependent. Designed to hold whole numbers Can be signed or unsigned:  12 -6 +3 Available in different sizes (number of bytes): short int, int, and long int Size of short int ≤ size of int ≤ size of long int
  25. 25. DECLARATION OF INTEGER VARIABLES  Declarations tell the compiler what variable names will be used and what type of data each can handle (store).  Variables of integer type can be defined - On separate lines: int length; int width; unsigned int area; - On the same line: int length, width; unsigned int area;
  26. 26. DATA TYPE: 2- CHARACTER Represents a single byte (8 bits) of storage. Used to hold characters like ‘d’ or ‘x’ etc.. Can be signed or unsigned Internally char is just a number Numerical value is associated with character via a character set. ASCII character set used in ANSI C Numeric value of character is stored in memory: MEMORY: CODE: letter char letter; letter = C; 67
  27. 27. DECLARATION OF CHARACTERVARIABLESVariables of character type can be defined: - On separate lines: char x; - On the same line: char x, y;
  28. 28. CHARACTER DATA A variable or a constant of char type can hold an ASCII character. When initializing a constant or a variable of char type, or when changing the value of a variable of char type, the value is enclosed in single quotation marks.Examples: const char star = *; char letter, one = 1;
  29. 29. DATA TYPES: 3- FLOATING-POINT A floating-point type is a number with a fractional part Represent typically 32 bit real numbers. Designed to hold real numbers 12.45 -3.8 All numbers are signed. Available in different sizes (number of bytes): float, double, and long double Size of float ≤ size of double ≤ size of long double
  30. 30. DECLARATION OF FLOATING POINTVARIABLES  Variables of floating point type can be defined: - On separate lines: double x; float y; long double z; - On the same line: double x, y; float y , e; long double z , r;
  31. 31. QUICK RESPONSE!  Question: char ch= ‘A’; what is the difference between: 1. printf(“%c”, ch); 3. printf(“%d”, ch);
  32. 32. Is void a kind of a data type?Yes or No??
  33. 33. DATA TYPE: 6-VOIDThe void data type has no values andno operations.
  34. 34. Operators &Expressions in CStack Overflow2011
  35. 35. ABOUT Operators and expressions• They decide the semantics of expression• Meaning of operator given in language system.• Expressions are formed by combining variables with operators and ALWAYS return a single value in C. i = 5; i < j; a = (a < b); C supports a rich set of operators that allow the programmer to manipulate variables
  36. 36. Operators- Types• Arithmetic Operators (+, -, *, /, %)• Relational Operators (<, >, <=, >=, ==, !=)• Logical Operators (&&, ||, !)• Bitwise Operators (&, |)• Assignment Operators (=)• Increment/Decrement Operators.• Conditional Operators.• Special operators.
  37. 37. ARITHMETIC OPERATORS Used for performing numeric calculations• Arithmetic calculations • Use * for multiplication and / for division • Integer division truncates remainder • 7 / 5 evaluates to 1 • Modulus operator(%) returns the remainder • 7 % 5 evaluates to 2• Operator precedence • Some arithmetic operators act before others (i.e., multiplication before addition) • Use parenthesis when needed • Example: Find the average of three variables a, b and c • Do not use: a + b + c / 3 • Use: (a + b + c ) / 3
  38. 38. Arithmetic Operators (Contd.) • Arithmetic Operators::C operation Arithmetic Algebraic C expression operator expressionAddition + f+7 f + 7Subtraction - p–c p - cMultiplication * bm b * mDivision / x/y x / yModulus % r mod s r % s
  39. 39. Arithmetic Operators (Contd.) • RULES OF OPERATOR PRECEDENCE::Operator(s) Operation(s) Order of evaluation (precedence)() Parentheses Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.*, /, or % Multiplication,Divi Evaluated second. If there are several, they are sion, Modulus evaluated left to right.+ or - Addition Evaluated last. If there are several, they are Subtraction evaluated left to right.
  40. 40. Arithmetic (summary)• Five simple binary arithmetic operators • + “plus”  c = a + b • - “minus”  c = a - b • * “times”  c = a * b • / “divided by” c = a/b • % “modulus” c = a % bQ. What are the values of c in each case above if 1. int a = 10, b = 2; 2. float a = 10, b = 2; 3. int a = 10; float b = 2; ??
  41. 41. Relational Operators Six basic operators for comparison of values in C. These are typically called relational operators: 1. > “greater than” 2. < “less than” 3. >= “greater than or equal to” 4. <= “less than or equal to” 5. == “is equal to” 6. != “is NOT equal to”• A relational operator compares two values of C built in data types such as char, int, float• Relational operators return Boolean values: • 0 if relation is FALSE • 1 if relation is TRUE
  42. 42. Relational (contd.)Standard algebraic C equality or Example of C Meaning of Cequality operator or relational condition conditionrelational operator operator (Syntax) Taking 2 variables ‘x’ and ‘y’Equality Operators= == x == y x is equal to yNOT = != x != y x is not equal to yRelational Operators> > x > y x is greater than y< < x < y x is less than y>= >= x >= y x is greater than or equal to y<= <= x <= y x is less than or equal to y
  43. 43. Relational (contd.)• Example: int x=44; int y=12; (x == y) // false... Returns 0 (x >= y) // true... Returns 1 (x != y) // true ... Returns 1
  44. 44. Relational Operator Compliments • Among the six relational operators, each one is the compliment of another operator such as,  > is compliment of <=  < is compliment of >=  == is compliment of !=
  45. 45. LOGICAL OPERATORS• Logical Operators are used to create compound expressions• There are three logical operators in C 1. || “logical OR” ♦ A compound expression formed with || evaluates to 1 (true) if any one of its components is true 2. && “logical AND” ♦ A compound expression formed with && evaluates to true if all of its components are true 3. ! “logical NOT” is used to define a compliment of any given expression or value or variableLogical operators, like relational operators, are typically used in conditional expressions 1. if ( (a == 1) && (b < 3) || (c == 1) ) etc.• However, these can also be used in regular expressions
  46. 46. Logical operator- Truth Table Operand-1 Operand-2 Op1 && Op2 Op1 | | Op2 (Op1) (Op2) (Logical AND) (Logical OR) Non-zero value Non-zero value 1 1 Non-zero value 0 0 1 0 Non-zero value 0 1 0 0 0 0 Some examples of Logical operators can be:: 2.if( age> 55 && salary < 1000) 3.If (number <0 || number >1000)
  47. 47. Relative Precedence• The relative precedence of the relational as well as logical operators is as follows::• HIGHEST ! > >= < <= == != &&• LOWEST ||
  48. 48. ASSIGNMENT OPERATORS• The operator symbol is the equal sign ( = ) • The expression on the right-hand side is evaluated and assigned to the left-hand variable. int x = 9;• Assignment operators are used to assign the result of an expression to a variable. C provides the facility of shorthand assignment operators of the form:: variable op= expression• Some examples are:: x= x+y can be written as x+=y a=a*(n+1) can be written as a *= n+1 z= z%d can be written as z%=d
  49. 49. INCREMENT/DECREMENT OPERATORS • In C, we have 2 very useful operators called the increment & decrement operators: • Increment : ++ adds 1 to the operand • Decrement : -- subtracts 1 from the operand • Both the operators are unary and take the following form:: ++x; OR x++; --y; OR y--;
  50. 50. Rules for ++ and – – operators• ++ and – – are unary operators; they require variable as their operands.• When postfix ++ (or – –) is used with a variable in an exp., the expression is evaluated first using the original value of the variable and then the variable’s value is accordingly incremented or decremented.• When prefix ++ (or – –) is used with a variable in an exp., firstly, the variable’s value is accordingly incremented or decremented and then the expression is evaluated using the new value of the variable.• The precedence and associativity if ++ & – – are same as that of unary + and unary –.
  51. 51. CONDITIONAL OPERATORS• The operators ? and : are called conditional operators as they are used to test the conditions in the conditional expressions.• Conditional expression :: • Format: <Expression 1> ? <Expression 2> : <Expression 3> • Example: x ? y : z Test Condition True expression False expression
  52. 52. Use of Conditional Operators  Now consider theseConsider the statements: following statements: a=80; a= 80; b=95; b= 95; z= (a>b) ? a : b; if(a>b) z=a; else Both the statements are resulting the same values. z=b; This is an example of usage of conditional expressions
  53. 53. BITWISE OPERATORS• Perform bitwise logical operations across individual bits of a value. • AND & • OR | x : 1 0 1 0 (binary) • XOR (exclusive OR) ^ y : 1 1 0 0 (binary) • NOT ~ x & y : 1 0 0 0 (binary) (1’s complement) x | y : 1 1 1 0 (binary)• Shifts are bitwise operators x ^ y : 0 1 1 0 (binary) • SHIFT LEFT << ~x : 0 1 0 1 (binary) • SHIFT RIGHT >> x << y shift x y-places to the left (add zeros) x >> y shift x y-places to the right (sign extend)
  54. 54. THE COMMA ( , ) OPERATOR• This operator is used to link the related expressions together• A comma-linked expression is evaluated from left to right & the value of the right most expression is the value of combined expression. Say, val = ( x=10, y=5, x+y) x is firstly assigned the value as 10, then y is assigned as 5 and then 15 (10+5) is being assigned to the val• This operator is used in for loops, while loops etc. • FOR loop for(i=0, j=1; i<=10 ; i++, j++); • WHILE loop while(c =getchar(), c!= ‘20’) • Interchanging values z=a, a=b, b=z;
  55. 55. THE SIZEOF OPERATOR• The sizeof operator is used with an operand to return the number of bytes the operand occupies. The operand may be a variable, a constant or a data type qualifier.• It’s a compile time operator.• Mainly used to find the length of arrays and structs when their sizes are unknown.• Also used to allocate memory spaces dynamically to different variables while any program execution.• For example:: k= sizeof (sum); j= sizeof(long int); w= sizeof(32767);
  56. 56. Rules of Precedence & Associativity • Precedence rule decides the order in which different operators are applied. • Associativity rule decides the order in which multiple occurrences of the same operator are applied.
  57. 57. OPERATOR PRECEDENCE/ASSOCIATIVITYOPERATORS (precedence from HIGHER to LOWER) ASSOCIATIVITY( ) [ ] -> . left to right! ~ ++ -- + - * & (type) sizeof right to left* / % left to right+ - left to right<< >> Bitwise left to right< <= > >= Relational left to right== != Relational left to right& Bitwise left to right^ Bitwise left to right| Bitwise left to right&& Logical left to right|| Logical left to right?: right to left= += -= *= /= %= &= ^= |= <<= >>= right to left, left to right