Copyright 1995 D. Hanson, K. Li & J.P. Singh Computer Science 217: Types Page 26 September 16, 1997 Types • The type of an object determinesthe values it can have and the operations that can be performed on it • Basic types char a “character”; typically a “byte” int an integer; typically a “word” float single-precision floating point double double-precision floating point • int qualifiers (optional) short int “smaller” intlong int “bigger” int , but not double precision • Unsigned integers: non-negative modulo where n is #bits/integer unsigned int unsigned short int unsigned char • Is char signed or unsigned? 2 nCopyright 1995 D. Hanson, K. Li & J.P. Singh Computer Science 217: Type Sizes Page 27 September 16, 1997 Type Sizes Note: C did not exist in 1964; this table just reflects typical sizes year 72–81 80–92 64–92 93–?computer DEC-10 PCsIBM360VAX68020SPARCMIPSR4000DEC Alpha char 7 8 8 8 short 18 16 16 16,32 int 36 16,32 32 32,64 type long 36 32 32 64 float 36 32 32 32 double 72 64 64 64 pointer 18 16, 32 32 64Copyright 1995 D. Hanson, K. Li & J.P. Singh Computer Science 217: Types of Constants Page 28 September 16, 1997 Types of Constants char 'a' character constant (single quote) '\035' character code 35 octal '\x29' character code 29 hexadecimal '\t' tab ( '\011' , do “ man ascii ” for details) '\n' newline ( '\012' ) '\\' backslash '\'' single quote '\b' backspace ( '\010' ) '\0' null character int 156 decimal constant 0234 octal 0x9c hexadecimal long 156L156l for sanity, use upper-case L float 15.6f1.56e1F double 15.6 “plain” floating point constants are double s15.6L15.6lCopyright 1995 D. Hanson, K. Li & J.P. Singh Computer Science 217: Constant Expressions Page 29 September 16, 1997 Constant Expressions • Const qualifier identifies read-only variables const double Pi = 3.14159;const double TwoPi = 2*3.14159; • Constant expressions are evaluated at compile time int p = 1 - 1;int p = 1/0, x = 1 ? 0 : 1/0; • Use constant expressionsto reduce the number of #define constantsto increase readabilityto improve changeability, e.g. #define MAXLINE 120...char buf[2*MAXLINE + 1];Copyright 1995 D. Hanson, K. Li & J.P. Singh Computer Science 217: Arrays Page 30 September 16, 1997 Arrays • Array declarations specify the number of elements, not the upper bound int digits[10]; digits is an array of 10 int s digits[0], digits[1], ..., digits[9] • Arrays may be indexed by any integer expression digits[f(x)/2 + BASE] • N o bounds checking! • Multi-dimensional arrays float matrix[3][4][5] a 3-dimensional array with elements • Arrays are stored in row-major order ; last subscript varies “fastest” matrix[0][0][0], matrix[0][0][1], ... 3 4 5 60=Copyright 1995 D. Hanson, K. Li & J.P. Singh Computer Science 217: Strings & Initialization Page 31 September 16, 1997 Strings & Initialization • “Strings” are arrays of characters " hello\n "the compiler always provides a terminating '\0' • Array length can be derived from initialization char hello[] = "hello\n"; is equivalent to char hello[7] = "hello\n";char hello[7] = { 'h', 'e', 'l', 'l', 'o', '\n', '\0' } • Ditto for arrays int x[] = { 1, 2, 3 };int y[][3] = {{ 1, 3, 5 },{ 2, 4, 6 },{ 3, 5, 7 },{ 4, 6, 8 }}; see K&R, sections 2.4 & 4.9 for more information 'h' 'e' 'l' 'l' 'o' '\12' '\0' these braces can be omittedwill be 4 — number of 3-element rowsCopyright 1995 D. Hanson, K. Li & J.P. Singh Computer Science 217: Enumerations Page 32 September 16, 1997 Enumerations • Enumerations associate constant values with identifiers enum boolean { NO, YES };enum color { RED, GREEN, BLUE }; • Values are generated and may be printed symbolically by debuggers • Values can be given and unspecified ones automatically continue enum escapes { BELL='\a', BACKSPACE='\b', TAB='\t'}; enum months { Jan=1, Feb, Mar, Apr, May, Jun, Jul,Aug, Sep, Oct, Nov, Dec }; • enum identifiers are int constants, but enumeration type may take less space sizeof NO is 4 bytes enum boolean flag; may occupy 1–4 bytes • enum identifiers should have no conflicts • What is the difference between enum and
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