C Programming Language (Chapter 2 of K&R) Variables and Constants

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1 C Programming Language (Chapter 2 of K&R) Types, Operators and Expressions Variables and Constants Basic objects manipulated by programs Declare before use: type var1, var2, int x, y, _X, x11, buffer; Name: combination of letters, _, and digits must start with a letter or _ avoid starting with _ (conflicts with library names) Case sensitive X and x are different 1

2 Data Types Few basic data types: char: single byte (holds one character) int: an integer (normally 4 bytes) float: single precision (normally 4 bytes) double: double precision (8 bytes on most sys) Qualifiers short/long apply to int signed/unsigned apply to char, int long double: extended-precision floating point See man -s4 limits Constants 1234, 1234L, 1234UL: int, long, unsigned long 12.34: float 0177, 0x1F: octal, hexadecimal 'x', '0', '\n', '\t', '\0': numeric value of the character in the machine s character set "this is a string": string constant enum boolean { NO, YES: enumeration const 2

3 Operators +, /, -, *, %: % works only for integral types ++, --: increment, decrement &,, ^, <<, >>, ~: bitwise and, or, exclusive or, left shift, right shift, one s complement (only with integral operands) >, >=, <, <=, ==,!=, &&, : relational and logical (numeric value of true is 1, false 0) &&, : evaluate left to right until truth value found!: Converts 0 to 1 and non-zero to 0 Type conversion Promote lower type to higher before operation long double (double (float (long int))) int short, char Unsigned operands: rules more complicated char: signed or unsigned? C language does not specify intchar: machine dependent (sign extension or..) printable characters are always positive 3

4 Type Conversion(continued) In the assignment x = y; the value of y is converted to the type of x; longer integers are converted to shorter by dropping high order bits int i; char c; i = c; c = i; /* no information is lost */ c = i; i = c; /* may loose information */ Explicit conversion using a cast Use cast when in doubt Assignment Op. & Expressions i = i+10 is equivalent to i += 10 += is called an assignment op. exp1 op= exp2 is equivalent to exp1 = (exp1) op (exp2) where exp1 and exp2 are expressions x *= y + 1 is equivalent to x = x * (y + 1) x = 2; y = 2; x *= y ; x has value 16 x = ; x >>= 2; x is x = ; x <<= 2; x is x = ; x = 0x02; x is

5 Control Flow (Ch 3) Specifies the order of computation C is similar to other languages, except perhaps for syntax An expression becomes a statement when followed by ; block: group of declarations and statements within braces {. No need for ; after if-else if (expression1) statement1 else if (expression2) statement2 else if (expression3) satement3 else statement4 Evaluate expression1 If no-zero execute statement1 else evaluate expression2 If no-zero execute statement2 else evaluate expression3 if non-zero exec statement3 otherwise exec statement4 5

6 Switch switch (expression) { case constexp1: statements case constexp2: statements default: statements Evaluate expression if case matches expression value, then execution starts at that point and falls through default is executed if non of the cases matches Precedence and Associativity Operators Associativity Comment () [] ->.! ~ * & (type) sizeof * / % + - << >> < <= > >= Unary + - * & ==!= & ^ exclusive or &&?: exp1? exp2 : exp3 = += -= *= /= %= &= ^= = <<= >>=, comma op(exp1,exp2) 6

7 Precedence and associativity int x = ; int i = 1, j = 2, k = 3; i += j -= k +=2; int x = 1;! x x ~ x x x x ^ x ( ( (2+ 3) - 1 ) + 4 ) i += ( j -= ( k+= 2)) (! x ) x ( 0 ) 1 1 (~ x ) x (11..10) in 2 s complement notation x ( x ^ x) #define PRINT(x) printf("%d\n", x) Example main() { int x, y, z; x = 2; y = 1; z = 0; x = x && y z; PRINT(x!y && z); x = y = 1; z = x++ - 1; PRINT(x); PRINT(z); z += -x y; PRINT(x); PRINT(z);

8 Loops (while and for) While (expression) statement for (exp1; exp2; exp3) statement While expression evaluates to non-zero, execute satement exp1; while(exp2) { statement exp3; for (;;) while(1) /* loop forever */ break and continue While ((c = getchar())!= EOF) { switch( c ) { case : case \n : case \t : nwhites++; break; default: others++; break causes innermost enclosing loop or switch to terminate for (i=0; i < n; i++){ if (a[i] < 0) continue; continue causes next iteration of the enclosing for or while to begin. 8

9 Example of & What does the following function do? 1 int mystery(unsigned short bits) 2 { 3 unsigned i, mask = 1 << 15, total =0; 4 for (i =1; i<=16; i++, bits <<= 1) 5 if (bits & mask) 6 ++total; 7 8 return (total % 2) == 0? 1 : 0; 9 Functions and Program Structures Functions are useful in several ways: help break large computing tasks to smaller units allow code to be reused conveniently and efficiently hide details of operations: encapsulate operations make it easier to maintain programs Everything is a function in C: no procedures All functions are linked together via main which controls the sequence in which units are executed 9

10 Function definition return-type function-name (argument declarations) { Declarations and statements int factorial (int n) { int i, f; f = 1; for (i=2; i < n; i++) f *= i; return(f); Invoking a function printf("%d\n", factorial(5)); Functions (continued) A C program is a set of external objects which are either variables or functions External variables are defined outside any function Functions are always external Communication between functions is by arguments, returned values, and external variables 1

11 Function prototyping Functions need to be declared before use Function definition can substitute for declaration A declaration states type of return value and types of arguments (this is also called prototype) int factorial(int); The C Preprocessor #include <filename> #include "filename"; Replace this with the content of filename. Search in the current directory, then system dependent places (/usr/include for example) #define identifier token_string #define id(id,, id) token_string replace all unquoted occurrences of identifier with token_string (long token strings can span a line using \) macros 1

UNIT- 3 Introduction to C++

UNIT- 3 Introduction to C++ C++ Character Sets: Letters A-Z, a-z Digits 0-9 Special Symbols Space + - * / ^ \ ( ) [ ] =!= . $, ; : %! &? _ # = @ White Spaces Blank spaces, horizontal tab, carriage