Introducing constants, variables and data types

1. Introducing constants, variables and data types March 31

2. Content • Warnings and errors • Constants • Data types`

3. Warnings and Errors • The GCC compiler can produce two kinds of diagnostics: errors and warnings. Each kind has a different purpose: • Errors report problems that make it impossible to compile your program. GCC reports errors with the source file name and line number where the problem is apparent. • Warnings report other unusual conditions in your code that may indicate a problem, although compilation can (and does) proceed. Warnings may indicate danger points where you should check to make sure that your program really does what you intend

4. Calculation of body mass index

5. Lets make errors on purpose Remove ; Remove &

6. Building a program with errors Notifies us about the syntactical error • Program does not compile because of the syntactical error Notifies us about the warning • Even thought program compiles and ready to run, it will not function correctly, thus pay attention to warnings carefully.

7. Data Variables and Constants variable constant • Some types of data are preset before a program is used and keep their values unchanged throughout the life of the program. These are constants. • Any attempt to modify a CONSTANT will result in error. • Other types of data may change or be assigned values as the program runs; these are variables.

8. Macro constant preprocessor directives Macro constant

9. Preprocessor • The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control. • In many C implementations, it is a separate program invoked by the compiler as the first part of translation. preprocessor compiler linker source code binary code Replaces all directives starting with # Analyzes code and generates object code Links object code with libraries • This semester we only use two preprocessor directives #include <header_file> will be substituted with the content of <header_file> #define <constant_name> <constant value> <constant_name> will be substituted with <constant value> throughout the source file

10. constspecifier • The other way to define constants is to use constspecifier. • What’s the difference between two types of constants? • The directive #define defines constant at compilation time • const<data_type> can be assigned during program execution, but only once!

11. Examples • Integer constants • Positive or negative whole numbers with no fractional part • Example: • constintMAX_NUM = 10; • constintMIN_NUM = -90; • Floating-point constants (float or double) • Positive or negative decimal numbers with an integer part, a decimal point and a fractional part • Example: • const double VAL = 0.5877e2; //(stands for 0.5877 x 102) • Character constants • A character enclosed in a single quotation mark • Example: • const char letter = ‘n’; • const char number = ‘1’; • printf(“%c”, ‘S’); • Output would be: S

12. Enumerated types Enumerated Types are a special way of creating your own Type in C. The type is a "list of key words". Enumerated types are used to make a program clearer to the reader/maintainer of the program.

13. Enumerated types • Enumerated Types are Not Strings • Enums are Not (Really) Integers • It turns out that enumerated types are treated like integers by the compiler. Underneath they have numbers 0,1,2,... etc. You should never rely on this fact

14. Basic Data Types • There are 4 basic data types : • int • float • double • char • int • used to declare numeric program variables of integer type • whole numbers, positive and negative • keyword: int intnumber; number = 12; -32,768 ~ 32,767 ( 16bit @ 16bit machine)

15. Basic Data Types 3.4e-38 ~ 3.4e38 ( 32bit @ 16bit machine) • float • fractional parts, positive and negative • keyword: float floatheight; height = 1.72; • double • used to declare floating point variable of higher precision or higher range of numbers • exponential numbers, positive and negative • keyword: double doublevaluebig; valuebig = 12E-3; 1.7e-308 ~ 1.7e308 ( 64bit @ 16bit machine)

16. Basic Data Types -128 ~ 127( 8bit @ 16bit machine) • char • equivalent to ‘letters’ in English language • Example of characters: • Numeric digits: 0 - 9 • Lowercase/uppercase letters: a - z and A - Z • Space (blank) • Special characters: , . ; ? “ / ( ) [ ] { } * & % ^ < > etc • single character • keyword: char charmy_letter; my_letter = 'U’; The declared character must be enclosed within a single quote!

17. Difference between integer and floating-point numbers An integer has no fractional part; Afloating-point number can have a fractional part. Floating-point numbers can represent a much larger range of values than integers can. For some arithmetic operations, such as subtracting one large number from another, floating-point numbers are subject to greater loss of precision. Floating-point values are often approximations of a true value. Floating-point operations are normally slower than integer operations.

18. Primary data types in C

19. Floating point representation float Simplified example

20. Double precision representation double C allows for a third floating-point type: long double. The intent is to provide for even more precision than double. However, C guarantees only that long double is at least as precise as double.

21. Hierarchy of Integer Types • C offers three adjective keywords to modify the basic integer type: short, long, and unsigned. • The type short intor, more briefly, short may use less storage than int, thus saving space when only small numbers are needed. Like int, short is a signed type. • The type longlong int, may use more storage than long, thus enabling you to express even larger integer values. Like int, longlong is a signed type. • The type unsigned int, or unsigned, is used for variables that have only nonnegative values. For example, a 16-bit unsigned intallows a range from 0 to 65535 in value instead of from –32768 to 32767.

22. Why Multiple Integer Types? The idea is to fit the types to the machine. The most common practice today is to set up long longas 64 bits, long as 32 bits, short as 16 bits, and intto either 16 bits or 32 bits, depending on the machine's natural word size. The minimum range for both short and intis –32,767 to 32,767, corresponding to a 16-bit unit, and the minimum range for long is –2,147,483,647 to 2,147,483,647, corresponding to a 32-bit unit.

23. When do you use the various inttypes? • Octal and hexadecimal constants are treated as type intunless the value is too large. Then the compiler tries unsigned int. If that doesn't work, it tries, in order, long, unsigned long, longlong, and unsigned longlong. First, consider unsigned types. It is natural to use them for counting because you don't need negative numbers, and the unsigned types enable you to reach higher positive numbers than the signed types. Use the long type if you need to use numbers that long can handle and that intcannot. Similarly, use long longif you need 64-bit integer values.

24. Integer Overflow The unsigned integer j is acting like a car's odometer. When it reaches its maximum value, it starts over at the beginning. The integer i acts similarly. The main difference is that the unsigned intvariable j, like an odometer, begins at 0, but the intvariable i begins at –2147483648

25. Octal and Hexadecimal • When dealing with a large number of bits, it is more convenient and less error-prone to write the binary numbers in hex or octal. VS C assumes that integer constants are decimal, or base 10, numbers. Octal (base 8) and hexadecimal (base 16) numbers are popular with many programmers. Because 8 and 16 are powers of 2, and 10 is not, these number systems occasionally offer a more convenient way for expressing computer-related values.

26. Displaying Octal and Hexadecimal dec = 100; octal = 144; hex = 64 dec = 100; octal = 0144; hex = 0x64 To display an integer in octal notation instead of decimal, use %o instead of %d. To display an integer in hexadecimal, use %x. If you want to display the C prefixes, you can use specifiers%#o, %#x, and %#X to generate the 0, 0x, and 0X prefixes, respectively

27. Printing short, long, long long, and unsignedtypes To print an unsigned intnumber, use the %u notation. To print a long value, use the %ldformat specifier. %hddisplays a short integer in decimal form, and %ho displays a short integer in octal form. Both the h and l prefixes can be used with u for unsigned types.

28. Printing short, long, long long, and unsigned types Note that using the %dspecifier for the unsigned variable produces a negative number! The reason for this is that the unsigned value 3000000000 and the signed value –129496296have exactly the same internal representation in memory on our system. When the value 65537 is written in binary format as a 32-bit number, it looks like 00000000000000010000000000000001. Using the %hdspecifier persuaded printf() to look at just the last 16 bits; therefore, it displayed the value as 1

29. The scanf function • Read data from the standard input device (usually keyboard) and store it in a variable. • General format: • scanf(“%d”, &variable); • Ampersand (&) operator : • C address of operator • it passes the address of the variable instead of the variable • tells the scanf() where to find the variable to store the new value or other specifiers depending on the variable type 0x124 0x128 0x12C 0x130 address: variable memory: &variable  0x128 4 bytes

30. The scanffunction • If you want the user to enter more than one value, you serialize the inputs. You can serialize input

31. Common Conversion Identifiers Common Conversion Identifier used in printf() and scanf() functions.

32. Nonprinting Characters • The single-quote technique is fine for characters, digits, and punctuation marks. • Some of the characters are nonprinting. • For example, some represent actions such as backspacing or going to the next line or making the terminal bell ring (or speaker beep) • There are two ways to define such variables. • Use reserved sequences • Use numeric codes form the character table (ASCII codes)

33. Partial listing of ASCII code

34. Printing Characters

35. The showf_pt.c Program The printf() function uses the %f format specifier to print type float and double numbers using decimal notation, and it uses %e to print them in exponential notation To correctly print out dip use %LF and %LE Then the output will be

36. Floating-Point Overflow and Underflow • This is an example of overflow—when a calculation leads to a number too large to be expressed. • The behavior for this case used to be undefined, but now C specifies that toobig gets assigned a special value that stands for infinity and that printf() displays either inf or infinity (or some variation on that theme) for the value. Suppose the biggest possible float value on your system is about 3.4E38 and you do this

37. Floating-Point Round-off Errors Output Compiler 0.00000  older gcc on Linux -13584010575872.00000  Turbo C 1.5 4008175468544.000000  clang on Mac OS, MSVC++ Take a number, add 1 to it, and subtract the original number. What do you get? You get 1. A floating-point calculation, such as the following, may give another answer:

38. Type Sizes

39. The typesize.c program The sizeof operator gives the amount of storage, in bytes, required to store an object of the type of the operand. This operator allows you to avoid specifying machine-dependent data sizes in your programs.