MORE ON DATA TYPES IN C

Transcription

1 KOM2741 Computer Programming Dr Muharrem Mercimek 1 MORE ON DATA TYPES IN C KOM2741 Computer Programming

2 KOM2741 Computer Programming Dr Muharrem Mercimek 2 Objectives In this presentation you will learn: More on data types Constants Type Conversions

3 KOM2741 Computer Programming Dr Muharrem Mercimek 3 C data types char usually 1 byte int usually the natural word size for a machine or OS (e.g., 16, 32, 64 bits) short int at least 2 bytes long int at least 4 bytes float usually 4 bytes double usually 8 bytes long double usually at least 8-bits The standard just states that a short int be at least 16-bits, a long int at least 32-bit, and short int int long int The standard says nothing about the size of floating-point numbers except that float double long double. The sizes are compiler specific. Related parameters e.g: INT_MIN can be found in standard headers limits.h and float.h

4 KOM2741 Computer Programming Dr Muharrem Mercimek 4 C data types General form of a declaration: <type qualifier, type specifiers> <type> <indentifier> = <value1>; type qualifiers: {const, volatile} type specifiers: {unsigned, signed} type: {char, short int (short), long int (long), float, double, etc.) Initialization with value1 is optional signed or unsigned can apply to char or any integer type signed type may represent negative values; the most-significant-bit (MSB) of the number is its signbit, and the value is typically encoded in 2 s-complement binary. 1 bit 31 bits int Integer. 4bytes signed: to unsigned: 0 to

5 KOM2741 Computer Programming Dr Muharrem Mercimek 5 C data types void in C (C++, Objective-C,...) void is a type, but it is special data type. You couldn't declare variable of type void. That's differ void from any other types. But you could declare pointer to void. A function having the return value as void, has no return value, or returns nothing If used as an argument for functions that have no arguments In C int main(void), you're stating that main takes no parameters, int main(), you're leaving open the possibility of executing main with some parameters. In C++ int main() as a function takes no parameters, so executing it with parameters is not possible

6 KOM2741 Computer Programming Dr Muharrem Mercimek 6 Constants The qualifier const means that the variable to which it refers cannot be changed. const int DoNotChangeThis = 5; DoNotChangeThis = 6; /* Error */ Constants can have different types and representations. 1. An integer constant: A constant of type long int : 234L; with L suffix. 3. A constant of type int with type specifiers unsigned : 234U with suffix U. UL specifies unsigned long. Octal numbers are preceded by a 0 and hex by 0x. Thus, 234 in decimal is equivalent to 0352 and 0xEA. It is important to remember that these three constants represent the same value ( in binary). int x = 234, y = 0352, z = 0xEA; printf("%d\t%o\t%x\n", x, x, x); // ea printf("%d\t%#o\t%#x\n", x, x, x); // xEA printf("%d\t%d\t%d\n", x, y, z); // C does not provide a direct binary representation. An Introduction to the C Programming Language and Software Design

7 KOM2741 Computer Programming Dr Muharrem Mercimek 7 Constants Floating-point constants: a decimal point after a number and 3.3 are of type double, f and 4.f are of type float, L is of type long double. Floating point numbers can also be written using scientific notation, 1.65e-2 (which is ). Constant expressions, ( ), are evaluated at compile-time. Character constants, a, \n, 7, are specified by single quotes. Character constants are in fact, not of type char, but of int. sizeof( Z ) is not one. ASCII character set, are represented by 0 to 127 with specific characters (e.g., the character Z is represented by integer value 90)

8 KOM2741 Computer Programming Dr Muharrem Mercimek 8 Constants There are certain characters that cannot be represented directly, but rather are denoted by an escape sequence. (%c use is either not possible, or cannot be noticed by the user) escape characters still represent single characters. String constants, such as Welcome to C" are delimited by quotes (the quotes are not part of the string constant) They are automatically appended with a terminating \0 character. In memory, the above string constant would comprise the following character sequence: Welcome to C\0.

9 KOM2741 Computer Programming Dr Muharrem Mercimek 9 Constants A symbolic constant is name that substitute for a sequence of character that cannot be changed. The character may represent a numeric constant, a character constant, or a string. When the program is compiled, each occurrence of a symbolic constant is replaced by its corresponding character sequence. They are usually defined at the beginning of the program. #define PI #define EXP #define PI defines a symbolic constant PI whose value is During pre-processing, all occurrences of the symbolic constant PI are replaced with the replacement text Note that the preprocessor statements begin with a #symbol, and are not end with a semicolon ;. Another form of symbolic constant is an enumeration, a list of constant integer values. enum { MONDAY=1, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY}; int y = MONDAY;

10 KOM2741 Computer Programming Dr Muharrem Mercimek 10 printf Conversion Specifiers %i or %d int %c char %f float %s string Important. A conversion specifier and its associated variable must be of matching type. If they are not, the program will either print garbage or crash. printf("%f", 52); /* Mismatch: floating point specifier, integer value */ printf("character values %5c %c %d \n", 'A', 'B', 'C'); printf("floating-point values %f %f \n", , 5e3); printf("floating-point values %6.1f %-6.1f %5.1f \n", f, f, f); printf("scientific notation %.2e %e %e %e \n", 3.556, 4.345, 2e3, 40.1f); printf(" %-16s \n", "Hello World"); return 0; Character values A B 67 Floating-point values Floating-point values Scientific notation 3.56e e e e+01 Hello World

11 KOM2741 Computer Programming Dr Muharrem Mercimek 11 Type Conversions and Casts When an operator has operands of different types, they are converted to a common type according to a small number of rules Type casting is a way to convert a variable from one data type to another data type. int sum = 19, count = 5; double mean; mean = (double) sum / count; printf("value of mean : %f\n", mean ); //Value of mean : the value of sum is first converted to type double and then divided by count yielding a double value.

12 KOM2741 Computer Programming Dr Muharrem Mercimek 12 Type Conversions and Casts For a binary expression such as a * b, the following rules are followed (assuming neither operand is unsigned): If either operand is long double, convert the other to long double. Otherwise, if either operand is double, convert the other to double. Otherwise, if either operand is float, convert the other to float. Otherwise, convert char and short to int, and, if either operand is long, convert the other to long. If the two operands consist of a signed and an unsigned version of the same type, then the signed operand will be promoted to unsigned, with strange results if the previously signed value was negative. The promotion from char to int is implementation-dependent char A simple example of type promotion is shown in the following code. short a = 5; int b = 10; float c = 23.1f; double d = c + a*b; short int (short) int long int (long) float double long double

13 KOM2741 Computer Programming Dr Muharrem Mercimek 13 Type Conversions and Casts Assignment to a narrower operand is possible, although information may be lost. Conversion to a narrower type should give a warning from good compilers. Conversion from a larger integer to a smaller one results in truncation of the higherorder bits, and conversion from floating-point to integer causes truncation of any fractional part. For example, int iresult = /5.0; The division 3/5.0 is promoted to type double so that the final summation equals 1.1 The result then is truncated to 1 in the assignment to iresult. Note, a conversion from double to float is implementation dependent and might be either truncated or rounded. Narrowing conversions should be avoided. For the cases where they are necessary, they should be made explicit by a cast. For example, int iresult = (int)( /5.0);