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Programming in C

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Programming in C

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  1. Variables, Controls, Arrays, Functions Programming in C

  2. Different Kinds of Languages • Java is an object-oriented programming (OOP) language • Problem solving centers on defining classes that model “things” like Trucks, Persons, Marbles, Strings, and CandyMachine • Classes encapsulate data (instance variables) and code (methods) C is a procedural language • Problem solving centers on defining functions that perform a single service like getValidInt( ), search( ) and inputPersonData( ). • Data is global or passed to functions as parameters • No classes

  3. Libraries • Because Java is an OOP language, its libraries consist of predefined classes that you can use in your applications • ArrayList, Scanner, Color, Integer • Because C is a procedural language, its library consists of predefined functions. • Char/string functions (strcpy, strcmp) • Math functions (floor, ceil, sin) • Input/Output functions (printf, scanf) • On-line C/Unix manual -- the “man” command • Description of many C library functions and Unix commands • Usage: man <function name> for C library functionsor man <command name> for Unix commands • man printf • man dir • Search for applicable man pages using the “apropos” command or “man -k” • Learn to use the man command using “man man”

  4. The C Standard • The first standard for C was published by the American National Standards Institute (ANSI) in 1989 and is widely referred to as “ANSI C” (or sometimes C89) • A slightly modified version of the ANSI C standard was adopted in 1990 and is referred to as “C90”. “C89" and "C90" refer to essentially the same language. • In March 2000, ANSI adopted the ISO/IEC 9899:1999 standard. This standard is commonly referred to as C99, and it is the current standard for the C programming language. • The C99 standard is not fully implemented in all versions of C compilers.

  5. C99 on GL • The GNU C compiler on the GL systems (gcc version 4.1.2) appears to support several useful C99 features. • These notes include those C99 features supported by gcc on GL since our course use that compiler. • These features will be noted as C99 features when presented.

  6. Hello World This source code is in a file such as hello.c /* file header block comment */ #include <stdio.h> int main( ) { // print the greeing ( C99 ) printf( “Hello World\n”); return 0; }

  7. Compiling on Unix Traditionally the name of the C compiler that comes with Unix is “cc”. However, the UMBC GL systems use the “GNU Compiler Collection” named “gcc” for compiling C (and C++) programs. The default name of the executable program that is created by gcc is a.out unix> gcc hello.c

  8. Compiler Options • -c • Compile only (create a .o file), don’t link (create an executable) gcc -c hello.c • -o filename • Name the executable filename instead of a.outgcc -o hello hello.c • -Wall • Report all warningsgcc -Wall hello.c • Use them together gcc -Wall -o hello hello.c • Note: the -ansi switch enforces the original ANSI C standard and disables C99 features.

  9. Compiling and Running a C Program unix> gcc -Wall -o hello hello.c printf.o Pre- processor (cpp) Compiler (cc1) Assembler (as) Linker (ld) hello.c hello.i hello.s hello.o hello Source program (text) Modified source program (text) Assembly program (text) Relocatable object programs (binary) Executable object program (binary) Execute your program by typing the name of the executableat the Unix prompt unix> hello

  10. Language Commonality • C and Java syntax have much in common • Some Data Types • Arithmetic operators • Logical Operators • Control structures • Other Operators • We assume that you are proficient in Java

  11. Integral Data Types • C data types for storing integer values are • int (the basic integer data type) • shortint (typically abbreviated just as short) • longint (typically abbreviated just as long) • longlongint (C99) • char (C does not have “byte”) • int should be used unless there’s a very good reason to use one of the others • char is stored in 1 byte • The number of bytes used by the other types depends on the machine being used

  12. Integral Type Sizes • The C standard is specifically vague regarding the size of the integral types • A shortint must not be larger than an int. • An int must not be larger than a longint. • A shortint must be at least 16 bits long. • An int must be at least 16 bits long. • A longint must be at least 32 bits long. • A longlongint must be at least 64 bits long. • The standard does not require that any of these sizes be necessarily different.

  13. Integral Specifiers • Each of the integral types may be specified as either • signed (positive, negative, or zero) • unsigned (positive or zero only) • signed is the default qualifier • Much more on this later

  14. Integral Variables • Each of the following is a valid variable declaration int age = 42; signed int age = -33; long area = 123456; short int height = 4; unsigned char IQ = 102; unsigned int length = 8282; unsigned long int SATscore = 800;

  15. Floating Point Data Types • C data types for storing floating point values (those with a decimal part) are • float, the smallest floating point type • double, a larger type with a larger range of values • longdouble, an even larger type with an even large range of values • double is typically used for all floating point values unless there’s a compelling need to use one of the others • Floating point variables may store integer values

  16. Size of Floating Point Type • A double variable can be marked as being a longdouble, which the compiler may use to select a larger floating point representation than a plain double. • The standard is unspecific on the relative sizes of the floating point values, and only requires a float not to be larger than a double, which should not be larger than a longdouble.

  17. Floating Point Declarations • Each of the following is a valid floating point variable declaration float avg = 10.6; double median = 88.54; double homeCost = 10000;

  18. Character Data Types • C has just one data type for storing characters • char, which is just one byte • Because a char is just one byte, C only supports the ASCII character set (more on this later)

  19. sizeof( ) • Because the sizes (number of bits/bytes) of the C data types are vaguely specified, C provides the sizeof() operator to determine the size of any data type (inbytes). • sizeof( ) should be used everywhere the size of a data type is required so that your code is portable to other hardware on which the size of the data types may be different. • On GL, • sizeof( short ) = 2 • sizeof( int ) = sizeof( long ) = 4 • sizeof (long long) = 8 • sizeof( float ) = 4 • sizeof( double ) = 8

  20. const Qualifier • Any of the variable types found above may be qualified as const. • const variables may not be modified by your code. Any attempt to do so will result in a compiler error. • Since they may not be modified, const variables must be initialized when declared const double PI = 3.1415; const int myAge = 39;

  21. Variable Declaration • ANSI C requires that all variables be declared at the beginning of the “block” in which they are defined, before any executable line of code. • C99 allows variables to be declared anywhere in the code (like Java and C++) • In any case, variables must be declared before they can be used.

  22. Arithmetic Operators Arithmetic operators are the same = is used for assignment +, -, (plus, minus) *, /, % (times, divide, mod) ++, -- (increment, decrement (pre and post)) Combinations are the same +=, -=, (plus equal, minus equal) *=, /=, %= (times equal, divide equal, mod equal) • Arithmetic Practice • Assignment Practice

  23. Boolean Data Type • ANSI C has no Boolean type • The C99 standard supports the Boolean data type • To use bool, true, and false, your code must include <stdbool.h> #include <stdbool.h> bool isRaining = false; if ( isRaining ) printf( “Bring your umbrella\n”);

  24. Type casting • C provides both implicit and explict type casting • Type casting is a means of temporarily treating one data type as if it were another • Int age = 42; • long longAge; • char charAge; • longAge = (long) age; • charAge = age;

  25. Logical Operators Logical operators are the same in C and Java and result in a Boolean value. • && (and) • || (or) • ==, != (equal and not equal) • <, <= (less than, less than or equal) • >, >= (greater than, greater than or equal) • Integral types may also be treated as Boolean expressions • Zero is considered “false” • Any non-zero value is considered “true” • Boolean Logic Practice

  26. Control Structures Both languages support these control structures which function the same way in C and Java • for loops • But NOT -- for (int i = 0; i < size; i++) • while loops • do-while loops • switch statements • if and if-else statements • braces ( {, } ) are used to begin and end blocks • Loop Practice

  27. Other Operators These other operators are the same in C and Java • ?: (tri-nary “hook colon”) int larger = (x > y ? x : y); • <<, >>, &, |, ^ (bit operators*) • <<=, >>=, &=, |=,^= • [ ] (brackets for arrays) • ( ) parenthesis for functions and type casting *much more on these later

  28. Arrays • Like most languages, C supports arrays as a basic data structure. • Array indexing starts with 0. • ANSI C requires that the size of the array be a constant • Declaring and initializing arrays int grades[44]; int areas[10] = {1, 2, 3}; long widths[12] = {0}; int IQs[ ] = {120, 121, 99, 154};

  29. Variable Size Arrays • C99 allows the size of an array to be a variable int nrStudents = 30; . . . int grades[nrStudents];

  30. 2-D Arrays • Like most languages, C supports multi-dimensional array • Subscripting is provided for each dimension • For 2-d arrays, the first dimension is the number of “rows”, the second is the number of “columns” in each row int board[ 4 ] [ 5 ]; // 4 rows, 5 columns int x = board[ 0 ][ 0 ]; // 1st row, 1st column int y = board[ 3 ][ 4 ]; // 4th (last) row, 5th (last) column

  31. #defines • The #define directive can be used to give names to important constants in your code. This makes your code more readable and more easily changeable. • The compiler’s preprocessor replaces every instance of the #define name with the text that it represents. • Note that there is no terminating semi-colon #define MIN_AGE 21 ... if (myAge > MIN_AGE) ... #define PI 3.1415 ... double area = PI * radius * radius; ...

  32. #define vs const • #define • Pro: no memory is used for the constant • Con: cannot be seen when code is compiled since they are removed by the pre-compiler • Con: are not real variables and have no type • const variables • Pro: are real variables with a type • Pro: can be examined by a debugger • Con: take up memory

  33. typedefs • C allows you to define new names for existing data types (NOT new data types) • This feature can be used to give application-specific names to simple types typedefint Temperature; typedefint[3] Row; • Or to give simple names to complex types - more on this later • Using typedefs makes future changes easier and makes the code more relevant to the application

  34. Enumeration Constants • C provides the enum as a list of named constant integer values (starting a 0 by default) • Behave like integers • Names in enum must be distinct • Often a better alternative to #defines • Example enum months { JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC }; ... enum months thisMonth; thisMonth = SEP; // preferred usage thisMonth = 42; // unfortunately, also ok

  35. Functions vs. Methods • Java classes include methods which can be called from any code with appropriate access (recall public methods) • C functions are like Java methods, but they don’t belong to any class. Functions are defined in a file and may be either global to your program or local to the file in which they are defined*. • Like Java methods, C functions • Have a name • Have a return type • May have parameters *more on this later

  36. More Functions • Before a function may be called, its “prototype” (aka signature -- name and parameters) must be known to the compiler so that it can verify that your code is calling the function correctly. • This is accomplished in one of two ways • Provide the entire function definition prior to the calling code • Provide the function prototype prior to the calling code and provide the function definition elsewhere • Unlike Java methods, a function in C is uniquely identified by its name. Therefore, there is no concept of method overloading in C as there is in Java. There can be only one main( ) function in a C application. • Our standards dictate that function names begin with and UPPERCASE letter

  37. A Simple C Program #include <stdio.h> typedef double Radius; #define PI 3.1415 /* given the radius, calculates the area of a circle */ double calcCircleArea( Radius radius ) { return ( PI * radius * radius ); } // given the radius, calcs the circumference of a circle double calcCircumference( Radius radius ) { return (2 * PI * radius ); } int main( ) { Radius radius = 4.5; double area = circleArea( radius ); double circumference = calcCircleCircumference( radius ); // print the results return 0; }

  38. Alternate Sample #include <stdio.h> typedef double Radius; #define PI 3.1415 /* function prototypes */ double calcCircleArea( Radius radius ); double calcCircleCircumference( Radius radius ); int main( ) { Radius radius = 4.5; double area = calcCircleArea( radius ); double circumference = calcCircleCircumference( radius ); // print the results return 0; } /* given the radius, calculates the area of a circle */ double calcCircleArea( Radius radius ) { return ( PI * radius * radius ); } // given the radius, calcs the circumference of a circle double calcCircleCircumference( Radius radius ) { return (2 * PI * radius ); }

  39. Typical C Program includes #include <stdio.h> typedef double Radius; #define PI 3.1415 /* function prototypes */ double calcCircleArea( Radius radius ); double calcCircleCircumference( Radius radius ); int main( ) { Radius radius = 4.5; double area = calcCircleArea( radius ); double circumference = calcCircleCircumference( radius ); // print the results return 0; } /* given the radius, calculates the area of a circle */ double calcCircleArea( Radius radius ) { return ( PI * radius * radius ); } // given the radius, calcs the circumference of a circle double calcCircleCircumference( Radius radius ) { return (2 * PI * radius ); } defines, typedefs, data type definitions, global variable declarationsfunction prototypes main() function definitions