Fundamental Data Types, Operators and Expressions

Kernighan/Ritchie:Kelley/Pohl:

Chapter 2Chapter 2, 3

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Lecture Overview

Variables and data types

Literals and constants

Operators and type conversions

Enumeration and typedef

Library functions – math, strings and I/O

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Identifiers

The name of a function, variable, or other language construct is called an identifier

Identifiers may contain letters, digits and the underscore ('_') character

An identifier may not begin with a digit

Reserved words cannot be used as identifiers

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Data Types

C has only two main data types: integer floating point

Each can be preceded by a qualifier,which changes its size or behavior: signed / unsigned short / long

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Integer Sizes

The basic integer data type is int

Its size is not defined as part of the language (unlike Java), and is machine dependant

The types long int and short int define different integer sizes

Short-cut names: long and short

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Signed and Unsigned Integers

The qualifiers signed and unsigned can be added before an integer type definition

By default, integers are signed

As with length qualifiers, the int can be dropped, and thus unsigned will definean unsigned int variable

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The char Data Type

All int types are multiple-byte

To define a single byte variable, the type char is used

char is just like any other integer type, and char and int variables may be assigned to each other freely

char is ASCII, not Unicode

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The sizeof Operator

The unary operator sizeof returns the number of bytes needed to store a variableof a given type:

It can also be used with a specific variable:

(Equivalent to using the variable's type)

sizeof (type)

sizeof (var)

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Data Type Sizes

#include <stdio.h>

int main() {

printf ("The size of some fundamental types:\n\n"); printf (" char:%3d byte \n", sizeof(char)); printf (" short:%3d bytes\n", sizeof(short)); printf (" int:%3d bytes\n", sizeof(int)); printf (" long:%3d bytes\n", sizeof(long)); printf (" unsigned:%3d bytes\n", sizeof(unsigned)); printf (" float:%3d bytes\n", sizeof(float)); printf (" double:%3d bytes\n", sizeof(double)); printf ("long double:%3d bytes\n", sizeof(long double));}

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Data Type Sizes

The results of running the previous program on one specific machine:

The size of some fundamental types:

char: 1 byte short: 2 bytes int: 4 bytes long: 4 bytes unsigned: 4 bytes float: 4 bytes double: 8 byteslong double: 12 bytes

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Lecture Overview

Variables and data types

Literals and constants

Operators and type conversions

Enumeration and typedef

Library functions – math, strings and I/O

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Literals

A literal is an explicit value appearing ina program

Literals can represent numbers, charactersor strings

Each literal belongs to a primitive type, and this type can be determined from its format

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Literal Types

Integer Decimal Hexadecimal Octal

Floating point Character String

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Literal Types

Any single character between single quotes is a character literal

A list of characters between double quotes is a string literal

Any unquoted number belongs either to one of the integer types, or to one of the floating point types

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Literal Types

A series of digits with no decimal point isan integer literal An integer literal is int by default, and can be

specified as long by adding an 'L' after it

A series of digits with a decimal point, or followed by an 'F' or by a 'D', is a floating point literal double by default, float if followed by an 'F'

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Literal Types – Examples

Literal

1788864L37.26637D87.363F26.77e3'c''&'"Hello""A&*/-?"

Data Type

intlongdoubledoublefloatdoublecharcharchar []char []

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Integer Literals In Different Number Bases

Just as the literal suffix defines the data type (int or long), the prefix defines the base (decimal, hexadecimal or octal)

A prefix of 0x stands for hexadecimal

A prefix of 0 stands for octal022, 065, 01

0xFF, 0xA1C, 0x25

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Literal Bases – Examples

Literal

1780xAA2502500x10001010

Base

DecimalHexadecimalDecimalOctalDecimalHexadecimalOctalDecimal

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Literal Bases – Examples

int main() { printf ("%d %x %o\n", 19, 19, 19); printf ("%d %x %o\n", 0x1c, 0x1c, 0x1c); printf ("%d %x %o\n", 017, 017, 017); printf ("%d\n", 11 + 0x11 + 011); printf ("%x\n", 2097151); printf ("%d\n", 0x1FfFFf); return 0;}

19 13 2328 1c 3415 f 17371fffff2097151

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String Literals

A string literal is an array of characters

The internal representation of a string hasa null character '\0' at the end

Therefore, the space required to hold a string is one byte more than its length

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Strings and Characters

An implementation of the library function that returns the length of a string:

int strlen (char s[]) {

int i = 0;

while (s[i] != '\0') i++;

return i;}

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Constants

A constant is a variable whose value cannot be changed

The compiler will issue a warning if you tryto change the value of a constant

In C, we use the const modifier to declarea constant

const int MONTHS_IN_YEAR = 12;

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const and #define

the const modifier creates a variable, with a type and with memory allocation

#define is not much more than a simple text replacement mechanism Saves memory, but has no type checking

const has additional uses, and can also be applied to function parameters or arrays

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Lecture Overview

Variables and data types

Literals and constants

Operators and type conversions

Enumeration and typedef

Library functions – math, strings and I/O

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Operators

C supports the same operators as Java: Arithmetic Assignment Increment / Decrement Bitwise Relational and Logical

Operator precedence rules are also similar

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Operators

Arithmetic operators: +, -, *, /, %

Assignment operators: =, +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=

Increment / Decrement operators: ++, --

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Operators

Bitwise operators: & (and), | (or), ~ (not), ^ (xor),<< (left shift), >> (right shift)

Relational and Logical operators: >, >=, <, <=, ==, !=, &&, ||

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Bitwise Operators

Bitwise operators work on specific bits

They have many uses, especially in low level operations Flags – each bit in an integer is a separate flag Compression – using non-standard data type sizes Communication protocols Computer graphics (turning pixels on or off)

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Bitwise Operators – Example

#include <stdio.h>

/* Get n bits starting at position p. */unsigned getbits (unsigned x, int p, int n) { return (x >> (p+1-n)) & ~(~0 << n);}

int main (int argc, char *argv[]) { /* Get bits 4,3,2 from 10010110. Result: 101. */ printf ("%d\n", getbits (150, 4, 3)); return 0;}

5

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Bitwise Operators – Example

Our goal is to start with bit 4, and take 3 bits to the right (bits 4, 3 and 2): The first shift pushes outside all bits to the right of

the desired section (bits 0 and 1) The second shift creates a mask with n bits in the n

rightmost places Using '&', all bits to the left of the desired section

are zeroed, and only the n rightmost bits are left

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Type Conversions

When operands of different types appearin an expression or in an assignment,the smaller is converted into the larger

Assignment or casting may also convert large types into smaller ones

Information loss will not cause a compilation error (possibly a warning)

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Converting float and int

#include <stdio.h>

int main() { int i; float f = 3.3;

i = f; f = i;

printf ("i: %d\n", i); printf ("f: %f\n", f);}

i: 3f: 3.000000

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Converting char and int

#include <stdio.h>

int main() {

int i; char c = 5;

i = c; c = i;

printf ("c equals: %d\n", c);}

c equals: 5

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Converting char and int

#include <stdio.h>

int main() {

int i = 1000; char c;

c = i; i = c;

printf ("i equals: %d\n", i);}

i equals: -24

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Converting char and int

#include <stdio.h>int main() { char c; int i;

for (i = 'a'; i <= 'z'; i++) printf ("%c", i) ; /* Print abc ... z */ printf ("\n");

for (c = 65; c <= 90; c++) printf ("%c", c) ; /* Print ABC ... Z */ printf ("\n");}

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

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Converting char and int

#include <stdio.h>

int atoi (char s[]) {

int i, n = 0; for (i = 0; s[i] >= '0' && s[i] <= '9'; i++) n = 10 * n + (s[i] - '0');

return n;}

int main() { printf ("%d\n", 1 + atoi ("345999"));}

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Type Conversion in Function Calls

Function calls can also trigger a conversion of the parameter or the return value#include <stdio.h>

void f (int p) { printf ("%d\n", p);}

int main() { f (3.3); return 0;}

3

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Lecture Overview

Variables and data types

Literals and constants

Operators and type conversions

Enumeration and typedef

Library functions – math, strings and I/O

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The use of typedef

typedef allows the programmer to associate a type with an identifier

Creates types that reflect the intended use

Can help in porting the program

The format is similar to that of a variable declaration:typedef type identifier

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typedef – Example

#include <stdio.h>

typedef int Inches, Feet;typedef char String[];

int main() { Feet input_feet; Inches input_inches; String message = "Please enter length:\n";

printf (message); scanf ("%d %d", &input_feet, &input_inches);

printf ("The length is: %d'%d\"\n", input_feet, input_inches);}

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typedef – Example

The same program without typedef:int main() {

int input_feet; int input_inches; char message[] = "Please enter length:\n";

printf (message); scanf ("%d %d", &input_feet, &input_inches);

printf ("The length is: %d'%d\"\n", input_feet, input_inches);}

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Enumeration Types

Enumeration types are another way of defining constants

Provides a way of defining a set of values Enumeration constants are of type int Each has a numeric value, starting with 0, and

increasing by 1 with each value Other values can be defined explicitly

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Enumeration Types

Defines an enumeration for week days

This defines the enumeration Fruit, and declares lunch as a variable of that type

The values of the constants are:APPLE=0,PEAR=1,ORANGE=3,LEMON=4

enum Day {SUN, MON, TUE, WED, THU, FRI, SAT};

enum Fruit {APPLE, PEAR, ORANGE = 3, LEMON} lunch;

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typedef and enum – Example

#include <stdio.h>enum Color {RED, GREEN, BLUE};typedef enum {TRUE = 1, FALSE = 0} Boolean;

int main() { enum Color favorite; Boolean is_favorite = TRUE;

printf ("sizeof(favorite): %d\n", sizeof(favorite)); favorite = GREEN; printf ("RED: %d\n", RED); printf ("favorite: %d\n", favorite);

if (is_favorite) printf ("Green is my favorite color!\n");}

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Lecture Overview

Variables and data types

Literals and constants

Operators and type conversions

Enumeration and typedef

Library functions – math, strings and I/O

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getchar() and putchar()

getchar() and putchar() are used to read and write single characters from/to the standard input/output

They are defined in stdio.h

In order to signal the end of a file, we need an additional value that is not a character

To hold this value, an int must be used

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getchar() and putchar() – Example

#include <stdio.h>

int main() { int c;

while ((c = getchar()) != EOF) if (c >= 'a' && c <= 'z') putchar (c + 'A' - 'a'); else putchar (c); return 0;}

> The date is: NOVEMBER 2006THE DATE IS: NOVEMBER 2006

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Additional Functions forReading Characters

getc() and putc() are similar to getchar() and putchar(), accept that they read from any file

FILE and EOF are defined in stdio.h Both functions return an EOF on failure

int getc (FILE *fp)

int putc (int c, FILE *fp)

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Reading Complete Lines

The standard I/O library also includes functions for handling complete lines

fgets() reads at most n-1 characters from the file associated with fp

The line is read into line, and a '\0' is inserted at the end, after the '\n'

char *fgets (char *line, int n, FILE *fp)

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Reading Complete Lines

fgets does not allocate memory to store the result, so line should point to a buffer large enough to contain the complete line Two additional spaces should be reserved beyond

the text itself, for '\n' and '\0'

If there are no more lines to read, then NULL is returned

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Example – Adding Line Numbersto a Text File

#include <stdio.h>

#define MAX_LINE_SIZE 80

int main() {

char buf[MAX_LINE_SIZE]; int line = 1;

while (fgets (buf, MAX_LINE_SIZE, stdin) != NULL) printf ("%4d %s", line++, buf);

return 0;}

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Formatted Input and Output with Files

The functions printf() and scanf() have special versions for accessing files

The file versions have the same format and arguments as the standard versions

is the same as

int fprintf (FILE *fp, const char *format, …)

int fscanf (FILE *fp, const char *format, …)

fprintf (stdout, …) printf (…)

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Formatted Input and Outputwith Strings

Similarly, the standard I/O functions have special versions that work with strings

The function sprintf() writes to its first argument instead of writing to the screen

sscanf() reads from the input string s

int sprintf (char *s, const char *format, …)

int sscanf (const char *s, const char *format, …)

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Formatted Input and Outputwith Strings – Example

#include <stdio.h>

int main() { char *str1 = "1234 12.5 hello"; char str2[80], str3[80]; float f; int i;

sscanf (str1, "%d %f %s", &i, &f, str2); sprintf (str3, "str %s, int %d, float %.2f", str2, i, f); printf ("Result: %s\n", str3);}

Result: str hello, int 1234, float 12.50

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String Functions

The standard library contains many functions for handling strings

The prototypes of these functions are defined in the header file string.h

An example we have seen earlier:

size_t is defined as an integral type

size_t strlen (const char *s)

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Mathematical Functions

The C language itself does not include any mathematical functions, but these can be obtained from the mathematics library

To use functions from the library, the math.h header should be included

Also, in some versions of UNIX, the -lm option must be passed to the compiler

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Mathematical Functions

Math functions accept double arguments, and return double values

Some functions from the math library: sqrt(), pow() exp(), log() sin(), cos(), tan()

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Mathematical Functions – Example

#include <stdio.h>#include <math.h>int main() { float x; printf ("Input x: "); scanf ("%f", &x); printf (" x = %.3f\n" " sqrt (x) = %.3f\n" " pow (x, x) = %.3f\n", x, sqrt (x), pow (x, x));}

Input x: 3 x = 3.000 sqrt (x) = 1.732 pow (x, x) = 27.000