C in a Nutshell A crash course in

‘C’ in a Nutshell A “crash course” in C. . . with designs for embedded systems by J. S. Sumey Part I: intro, variables, constants, operators ver. Feb 2018

REFERENCE: The C Programming Language (2 nd ed. ) Brian W. Kernighan Dennis M. Ritchie Prentice Hall Software Series 'C' in a Nutshell by J. Sumey 2 of 27

Low-Level (Assembly) Programming pros: n object code is smaller and runs faster w important in embedded systems! n programmer has total control over system hardware cons: n need to know processor and hardware intimately more tedious & time consuming not portable! 'C' in a Nutshell by J. Sumey 3 of 27

High-Level Programming pros: n n source code is highly portable more streamlined development, quicker w increased programmer productivity n n n support of structured design techniques more readable code, easier maintenance better math handling support cons: n increased overhead 'C' in a Nutshell by J. Sumey 4 of 27

“Mixed” Approach can use HLL like ‘C’ for bulk of project and use assembly for select parts n n n time-sensitive functions interrupt handling special instructions, ex: fuzzy logic creates linkage issues n n calling assembly routines from C parameter passing & return results 'C' in a Nutshell by J. Sumey 5 of 27

C Background created in ‘ 70 s by Dennis Ritchie at Bell Labs a general-purpose “systems” programming language, multi-domain n applications compilers operating systems platform & architecture independent standardized in late ‘ 80 s by ANSI “ANSI C” is actually known as a mid-level language most commonly used language in industry 'C' in a Nutshell by J. Sumey 6 of 27

Overview 1 a ‘typed’ language n n fundamental: characters, integers, floating-point derived: pointers, arrays, structures, unions “basic” arithmetic & logical operations only typical control-flow constructs n n statement grouping decision selection looping 'C' in a Nutshell by J. Sumey 7 of 27

Overview 2 functions: n n may return anything (or nothing) no nesting may be recursive may exist in separate source files compiled individually or combined into a single file variable scope (declarations, actually): n n n local to a function local to a source file, global to all functions within global to entire program 'C' in a Nutshell by J. Sumey 8 of 27

Overview 3 uses a “preprocessor” during compilation n macro substitution include files conditional compilation depends on libraries for everything else! n n n input / output file access composite object manipulation w i. e. , arrays, lists, strings n dynamic memory allocation 'C' in a Nutshell by J. Sumey 9 of 27

I. Data Types & Operations - representation of information & how to manipulate it

Constants - 1 integers n use suffix to override default int w ex: 99999 L – forces interpretation as long w ex: 32767 U – forces unsigned interpretation n prefixes to override default base (10) w ex: 037 = 0 x 1 f = 31 w ex: 0 XFUL = ? ? ? w some compilers also support binary constants: #define MASK 0 b 11110000 floats n contain ‘. ’ or ‘e’, default is double w ex: 1 e-1 L – forces long interpretation 'C' in a Nutshell by J. Sumey 11 of 27

Constants - 2 characters n a single character within single quotes w ex: ‘A’ = 0 x 41 = 65 n can represent certain control characters via “escape sequences” w ex: ‘n’, ‘b’, ‘f’, ‘g’, ‘r’, ‘t’, ‘\’ n can also represent characters in octal & hex w ex: #define LF ‘12’ w ex: #define CR ‘ x 0 d’ 'C' in a Nutshell by J. Sumey 12 of 27

Constants - 3 sting literals n n zero or more characters within double quotes terminating null byte (‘’) is assumed w ex: “a 21 character string” (requires how many bytes? ) gotcha: n ‘t’ “t” 'C' in a Nutshell by J. Sumey 13 of 27

Variables represent named storage locations in memory must be declared before use n associates a data type to the variable letters, numbers, & underscore n n n must start with letter or ‘_’ library routines typically start variables with ‘_’ convention: all UPPERCASE for symbolic constants; lower or mixed upper/lower for variables minimum 31 characters significant don’t use reserved words (if, else, int, etc. ) 'C' in a Nutshell by J. Sumey 14 of 27

Data Types Basic data types: n char – holds a single character (ASCII) w typically consumes 1 byte per char w has same characteristics as ints n int – integer only number w typically 16 or 32 bits, depends on architecture n float – ‘single precision’ floating point w typically 32 bits, depends on architecture n double – ‘double precision’ floating point w typically 64 bits, depends on architecture 'C' in a Nutshell by J. Sumey 15 of 27

Data Type ‘Qualifiers’ modify the basic properties of the data type n long & short – apply to integers to force them to more or less dynamic range w ex: short int loopctr; w ‘int’ may be omitted n signed & unsigned – applies to chars & ints w ex: unsigned char uc; range of ‘uc’ is 0. . 255 w ex: signed char sc; range of ‘sc’ is -128. . +127 n long double – extended-precision floating point standard headers define sizes for given system n <limits. h> & <float. h> 'C' in a Nutshell by J. Sumey 16 of 27

Sample program: sizes. c #include <stdio. h> #include <limits. h> #include <float. h> main() { printf( "n--- SIZES OF BASIC DATA TYPES ON A COLDFIRE v 1 ---nn" ); printf( "number of bits in a char: %in", CHAR_BIT ); printf( "range of a unsigned char: %u. . %un", 0, UCHAR_MAX ); printf( "range of a signed char: %i. . %in", SCHAR_MIN, SCHAR_MAX ); printf( "range of a plain ol char: %i. . %in", CHAR_MIN, CHAR_MAX ); puts( "" ); printf( "number of bits in a short: %in", sizeof(short)*8); printf( " range of a short integer: %i. . %in", SHRT_MIN, SHRT_MAX ); printf( " an unsigned short: %u. . %un", 0, USHRT_MAX ); puts( "" ); printf( " number of bits in a int: %in", sizeof(int)*8 ); printf( " range of a plain integer: %i. . %in", INT_MIN, INT_MAX ); printf( " an unsigned int: %u. . %un", 0, UINT_MAX ); puts( "" ); printf( " number of bits in a long: %in", sizeof(long)*8 ); printf( " range of a long integer: %li. . %lin", LONG_MIN, LONG_MAX ); printf( " an unsigned long: %lu. . %lun", 0 L, ULONG_MAX ); puts( "" ); printf( " number of bits in a long: %in", sizeof(long)*8 ); printf( " range of a long int: %lli. . %llin", LLONG_MIN, LLONG_MAX ); printf( " an unsigned long: %llu. . %llun", 0 LL, ULLONG_MAX ); puts( "" ); printf( " number of digits in a float: %in", FLT_DIG ); printf( " range of a plain ol’ float: %E. . %En", FLT_MIN, FLT_MAX ); puts( "" ); printf( "number of digits in a double: %in", DBL_DIG ); printf( " range of a plain ol’ double: %. 15 E. . %. 15 En", DBL_MIN, DBL_MAX ); } 'C' in a Nutshell by J. Sumey 17 of 27

Sample run on a Cold. Fire v 1 MCU --- SIZES OF BASIC DATA TYPES ON A COLDFIRE v 1 --number of bits in a range of a unsigned range of a plain ol char: 8 0. . 255 -128. . 127 0. . 255 number of bits in a short: 16 range of a short integer: -32768. . 32767 an unsigned short: 0. . 65535 number of bits in a int: 32 range of a plain integer: -2147483648. . 2147483647 an unsigned int: 0. . 4294967295 number of bits in a long: 32 range of a long integer: -2147483648. . 2147483647 an unsigned long: 0. . 4294967295 number of bits in a long: 64 range of a long int: -9223372036854775808. . 9223372036854775807 an unsigned long: 0. . 18446744073709551615 number of digits in a float: 6 range of a plain ol’ float: 1. 175494 E-38. . 3. 402823 E+38 number of digits in a double: 15 range of a plain ol’ double: 2. 225073858507201 E-308. . 1. 797693134862316 E+308 'C' in a Nutshell by J. Sumey 18 of 27

Data Types for Embedded Systems very useful in embedded systems: n byte-sized (8 -bit) data w Byte, uchar, uint 8, byte: 0. . 255 w s. Byte, schar, sint 8: -128. . +127 n 16 -bit data w Word, uint 16, word: 0. . 65535 w s. Word, sint 16: -32768. . +32767 n 32 -bit data w LWord, ulong, uint 32, dword: 0. . 4294967295 w s. LWord, slong, sint 32: -2147483648. . 2147483647 n Boolean w bool: TRUE/FALSE n these are defined in stdtypes. h, derivative. h, etc. 'C' in a Nutshell by J. Sumey 19 of 27

“Extended” Data Types additional data types derived from or extending the basic types: n n n array pointer structure union function will save for part III 'C' in a Nutshell by J. Sumey 20 of 27

Variable ‘Storage’ Attributes define where variables are stored and how they may be used / accessed n n n auto (default) – in a “stack frame” register – kept in a processor register if possible const – a variable that doesn’t change after initialization w should be stored in ROM n volatile – a variable that can change “on its own” w I/O registers, semaphores n extern – a variable defined outside the module it is referenced from 'C' in a Nutshell by J. Sumey 21 of 27

Declarations variables must be declared before use specifies a data type to each variable n n ex: int first, last, inc; ex: short Circuit; may also include an initializer n ex: char esc = ‘ x 1 b’; the “const” qualifier declares a read-only variable (cannot be subsequently changed) n ex: const float pi = 3. 14159; 'C' in a Nutshell by J. Sumey 22 of 27

Operators - 1 arithmetic n +, -, *, /, % (modulus, ints only) equality n == (equal), != (not equal) relational n <, <=, =>, > logical – normally used in if statements n && (and), || (or), ! (not) 'C' in a Nutshell by J. Sumey 23 of 27

Operators - 2 increment / decrement n n ++, -be careful of prefix vs. postfix use! bitwise n n perform bit manipulation on char/integers only & (AND), | (OR), ^ (EOR) << (shift left), >> (shift right) ~ (1’s complement) these operators can be very useful for embedded programming! n ex… 'C' in a Nutshell by J. Sumey 24 of 27

Assignment Operators many binary operators have a corresponding “assignment operator” n n n e 1 op= e 2 is equivalent to e 1 = e 1 op e 2 ex: step += 2 this works for +, -, *, /, %, <<, >>, &, ^, | increases efficiency in embedded programming! (how? ) n n ex: porta |= 4; ex: portb &= ~4; 'C' in a Nutshell by J. Sumey 25 of 27

Conditional Expressions uses the ternary operator “? : ” and three expressions n n expr 1 ? expr 2 : expr 3 means: expr 2 if expr 1 is true (non-0), else expr 3 ex: z = (a < b) ? a : b; is equivalent to: if (a < b) z = a; else z = b; i. e. , z = min(a, b) !! 'C' in a Nutshell by J. Sumey 26 of 27

Precedence PREC. hi determines order of expression evaluation; hence result! association determines binding of operators may always be overridden with parens n ex: if (porta & 0 x 80 == 0) bomb = 17 / 0; OOPS! what’s really wrong here? lo 'C' in a Nutshell by J. Sumey OPERATOR ASSOC. () [] ->. l-to-r ! ~ ++ -- + - (unary) * & (type) sizeof r-to-l */% l-to-r + - (binary) l-to-r << >> l-to-r < <= >= > l-to-r == != l-to-r & l-to-r ^ l-to-r | l-to-r && l-to-r || l-to-r ? : r-to-l = op= r-to-l , l-to-r 27 of 27