2 1. variables & data types
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This document discusses variables and fundamental data types in C programming. It explains that variables are used to store temporary values during program execution and must be declared before use. It also covers the different fundamental data types like int, char, float, and double, and how they are represented and used. Integer, floating point, and character constants are also explained.
![Variables
Variables Naming Rule
– Composed of English alphabets, numbers, _(underbar)
– First character should be an English alphabet or _(underbar)
[Ex]
available variable name: times10, get_next_char, _done
Not available variable name: 10times, get-next-char, int
– maximum length: 255
– Reserved words are not available as variable names
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![Integer Constants
Integer Constants :
– In C, integer type is represented as Decimal, Octal,
Hexadecimal
[Ex] 17 /* decimal integer constant */
017 /* octal integer constant : 17(8) = 15 */
0x17 /* hexadecimal integer constant 17(16)= 23 */
-17 /* negative decimal integer constant */
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![The Data Type char
char type
– 8 bits for all machines
– Can represent 256 characters
– Can store a character or a small integer number
[Ex]
printf(“%c”, ‘a’ ); /* a is printed */
printf(“%c%c%c”, ‘A’, ‘ B’, ‘C’ ); /* ABC is printed */
printf(“%c”, 97 ); /* a is printed */
printf(“%c”, ‘a’+1 ); /* b is printed */
printf(“%d”, ‘a’ ); /* 97 is printed */
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![The Data Type char
char variables can be handled as int variables
[Ex]
char c; int i;
for ( i = ‘a’ ; i <= ‘z’; ++i )
printf(“%c”, i); /* abc … z is printed */
for ( c = 65; c <= 90 ; ++c )
printf(“%c”, c); /*ABC … Z is printed */
for ( c = ‘0’; c <= ‘9’ ; ++c )
printf(“%d ”, c); /* 48 49 50… 57 is printed */
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![The Data Type char
[Ex]
char c;
c= ‘A’+5;
F 70
printf(“%c %dn”, c, c);
[Ex]
c = ‘A’;
B 66
c++;
printf(“%c %dn”, c, c);
[Ex]
for( c = ‘A’; c <= ‘Z’; c++ ) A B C D E…Z
printf(“%ct”,c);
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![The Floating Types
float, double, long double
– Store real number data
– Store approximated values (Not exact values)
– Exponential notation possible
[Ex] 1.234567e5 = 1.234567 x 105 integer : 1
fraction : 234567
exponent : 5
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![The Floating Types
float
– 4bytes memory allocation (4 byte machine)
– Can store 6~7 significant digits
– Range of float type: 10-38 ~ 1038
[Ex] float a = 123.451234;
double
– 8bytes memory allocation
– Can store 15~16 significant digits
– Range of double type : 10-308 ~ 10308
[Ex] double a = 123.45123451234512345;
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![Floating Constants
Float Constants :
– Represented by decimal point numbers
– Represented by exponential forms
[Ex] 57.0 /* Decimal point */
5.70E1 /*Exponential form */
.57e+02
570.e-01
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![Casts
Casts
– Operand type converted in expression
– (type)expression
[Ex1] int a=3, b=2;
double c = a / b;
printf(“c=%fn”, c); c=1.000000
[Ex2] int a=3, b=2;
double c = (double) a / b;
printf(“c=%fn”, c);
c=1.500000
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2 1. variables & data types
- 1. Variables & Fundamental Data Types
- 2. Structure of C program Start with #include <..> #include <stdio.h> void main() All statements locate { between “void main() {“ int x ; and “}” scanf( “%d”, &x ) ; All statements end with “;” printf( “%dn”, x*x ) ; return ; Case sensitive } – “Printf” and “printf” are not the same 2
- 3. Structure of C program #include <stdio.h> void main() Variable declaration { int x ; Input scanf( “%d”, &x ) ; printf( “%dn”, x*x ) ; Output return ; } 3
- 4. Variables Variables – Memory space for storing temporary values during the executing program – Variable must be declared before use – Variables are created in memory during the executing program #include <stdio.h> … void main() inches { feet int inches, feet, fathoms; fathoms … … } 4
- 5. Variables Variables Naming Rule – Composed of English alphabets, numbers, _(underbar) – First character should be an English alphabet or _(underbar) [Ex] available variable name: times10, get_next_char, _done Not available variable name: 10times, get-next-char, int – maximum length: 255 – Reserved words are not available as variable names 5
- 6. Variables Reserved Words – Words reserved for C language Keywords auto do goto signed unsigned break double if sizeof void case else int static volatile char enum long struct while const extern register switch continue float return typedef default for short union 6
- 7. Variables What is int ahead of variables? #include <stdio.h> void main() Types of values { variables can store int inches, feet, fathoms; … } 7
- 8. The Fundamental Data Types Data Types in C Fundamental data types char signed char unsigned char signed short int signed int signed long int unsigned short int unsigned int unsigned long int float double long double – ‘signed’ keyword can be ignored • int and signed int, long and signed long, each pair has the same meaning – ‘int’ keyword can be ignored in short int, long int, unsigned int • Simply short, long, unsigned are OK 8
- 9. The Data Type int int : – 2 byte machine : -32768(-215) ~ 32767(215-1) – 4 byte machine : -2147483648(-231) ~ 2147483647(231-1) – 8 byte machine : -2147483648(-231) ~ 2147483647(231-1) short – 2 byte machine : -32768(-215) ~ 32767(215-1) – 4 byte machine : -32768(-215) ~ 32767(215-1) – 8 byte machine : -32768(-215) ~ 32767(215-1) long – 2 byte machine : -2147483648(-231) ~ 2147483647(231-1) – 4 byte machine : -2147483648(-231) ~ 2147483647(231-1) – 8 byte machine : -263 ~ (263-1) 9
- 10. The Integral Types unsigned: positive integer only – Range of unsigned int (0 ~ 2wordsize-1) • 2 byte machine: 0 ~ 65535(216-1) • 4 byte machine: 0~ 42949647295(232-1) • 8 byte machine: 0~ 42949647295(232-1) – Range of unsigned long • 2 byte machine: 0~ 42949647295(232-1) • 4 byte machine: 0~ 42949647295(232-1) • 8 byte machine: 0 ~ (264-1) 10
- 11. The Integral Types Binary representation of 2 bytes int Case of int Case of unsinged int 0000 0000 0000 0000 -> 0 0000 0000 0000 0000 -> 0 0000 0000 0000 0001 -> 1 0000 0000 0000 0001 -> 1 0000 0000 0000 0010 -> 2 0000 0000 0000 0010 -> 2 0000 0000 0000 0011 -> 3 0000 0000 0000 0011 -> 3 … … 0111 1111 1111 1110 -> 215-2 0111 1111 1111 1110 -> 215-2 0111 1111 1111 1111 -> 215-1 0111 1111 1111 1111 -> 215-1 1000 0000 0000 0000 -> -215 1000 0000 0000 0000 -> 215 1000 0000 0000 0001 -> -215+1 1000 0000 0000 0001 -> 215+1 1000 0000 0000 0010 -> -215+2 1000 0000 0000 0010 -> 215+2 … … 1111 1111 1111 1101 -> -3 1111 1111 1111 1101 -> 216-3 1111 1111 1111 1110 -> -2 1111 1111 1111 1110 -> 216-2 1111 1111 1111 1111 -> -1 1111 1111 1111 1111 -> 216-1 11
- 12. The Integral Types Example : 4 byte machine 2147483645 int i = 2147483645, j ; 2147483646 for( j = 0 ; j < 5 ; j++ ) 2147483647 printf( “%dn”, i + j ) ; -2147483648 -2147483647 2147483645 unsigned int i = 2147483645, j ; 2147483646 for( j = 0 ; j < 5 ; j++ ) 2147483647 printf( “%un”, i + j ) ; 2147483648 2147483649 12
- 13. The Integral Types Example : 4 byte machine -1 4294967295 int i = -1 ; -1 -1 unsigned u = -1 ; 4294967295 4294967295 printf( “%d %un”, i, u ) ; printf( “%d %dn”, i, u ) ; printf( “%u %un”, i, u ) ; 13
- 14. Integer Constants Integer Constants : – In C, integer type is represented as Decimal, Octal, Hexadecimal [Ex] 17 /* decimal integer constant */ 017 /* octal integer constant : 17(8) = 15 */ 0x17 /* hexadecimal integer constant 17(16)= 23 */ -17 /* negative decimal integer constant */ 14
- 15. Integer Constants Example #include <stdio.h> 17 15 23 int main(void) { int i = 17, j = 017, k =0x17 ; printf( “%d %d %dn”, i, j, k ) ; return 0 ; } #include <stdio.h> 15 17 f F int main(void) { int i = 15; printf( “%d %o %x %Xn”, i, i, i, i ) ; return 0 ; } 15
- 16. The Data Type char char type – 8 bits for all machines – Can represent 256 characters – Can store a character or a small integer number [Ex] printf(“%c”, ‘a’ ); /* a is printed */ printf(“%c%c%c”, ‘A’, ‘ B’, ‘C’ ); /* ABC is printed */ printf(“%c”, 97 ); /* a is printed */ printf(“%c”, ‘a’+1 ); /* b is printed */ printf(“%d”, ‘a’ ); /* 97 is printed */ 16
- 17. The Data Type char char variables can be handled as int variables [Ex] char c; int i; for ( i = ‘a’ ; i <= ‘z’; ++i ) printf(“%c”, i); /* abc … z is printed */ for ( c = 65; c <= 90 ; ++c ) printf(“%c”, c); /*ABC … Z is printed */ for ( c = ‘0’; c <= ‘9’ ; ++c ) printf(“%d ”, c); /* 48 49 50… 57 is printed */ 17
- 18. The Data Type char [Ex] char c; c= ‘A’+5; F 70 printf(“%c %dn”, c, c); [Ex] c = ‘A’; B 66 c++; printf(“%c %dn”, c, c); [Ex] for( c = ‘A’; c <= ‘Z’; c++ ) A B C D E…Z printf(“%ct”,c); 18
- 19. The Data Type char Escape sequence Nonprinting and hard-to-print characters Name of character Written in C Integer value alert a 7 backslash 92 backspace b 8 carriage return r 13 double quote ” 34 formfeed f 12 horizontal tab t 9 newline n 10 null character 0 0 single quote ’ 39 vertical tab v 11 19
- 20. The Floating Types float, double, long double – Store real number data – Store approximated values (Not exact values) – Exponential notation possible [Ex] 1.234567e5 = 1.234567 x 105 integer : 1 fraction : 234567 exponent : 5 20
- 21. The Floating Types float – 4bytes memory allocation (4 byte machine) – Can store 6~7 significant digits – Range of float type: 10-38 ~ 1038 [Ex] float a = 123.451234; double – 8bytes memory allocation – Can store 15~16 significant digits – Range of double type : 10-308 ~ 10308 [Ex] double a = 123.45123451234512345; 21
- 22. The Floating Types Float type operation – Up to 6~7 significant digits (also approximation) float f1 = 0.1234567, f2 = 0.00000008 ; f1 + f2 == ? float f1 = 12345670.0, f2 = 8.0 ; f1 + f2 == ? float f1 = 123.4567, f2 = 100000.0 ; f1 + f2 == ? 22
- 23. Floating Constants Float Constants : – Represented by decimal point numbers – Represented by exponential forms [Ex] 57.0 /* Decimal point */ 5.70E1 /*Exponential form */ .57e+02 570.e-01 23
- 24. Floating Constants Example 57.0 57.0 57.0 57.0 #include <stdio.h> int main(void) { float f=57.0, g=5.70E1, h=.57e+02, i=570e-01 ; printf( “%.1f %.1f %.1f %.1fn”, f, g, h, i ) ; return 0 ; } 57.0 5.7e+001 5.7E+001 #include <stdio.h> int main(void) { float f=57.0, g=57.0, h=57.0 ; printf( “%.1f %.1e %.1En”, f, g, h ) ; return 0 ; } 24
- 25. Data Types: Operations with Different Type Rounded up, Comparison Chopping float f = 1.23456789 ; int n1, n2; float f = 1.2 ; if( f == 1.23456789 ) printf( “Yesn” ) ; n1 = f + 0.5 ; else n2 = f ; printf( “Non” ) ; 25
- 26. Data Types: Operations with Different Type Operation between int and float – Arithmetic operation of int and int results in int – Arithmetic operation of float and float results in float – Arithmetic operation of int and float results in float – Comparison operations between two types are done as you expect 2 + 1 == ? 2.0 + 1.0 == ? 2 + 1.0 == ? 2<1 ? 2 * 1 == ? 2.0 * 1.0 == ? 2.0 * 1 == ? 2.0 > 1 ? 3 / 2 == ? 3.0 / 2.0 == ? 3 / 2.0 == ? 2.0 <= 1.0 ? 3 % 2 == ? 3.0 % 2.5 == ? 3 % 2.0 == ? 26
- 27. Casts Casts – Operand type converted in expression – (type)expression [Ex1] int a=3, b=2; double c = a / b; printf(“c=%fn”, c); c=1.000000 [Ex2] int a=3, b=2; double c = (double) a / b; printf(“c=%fn”, c); c=1.500000 27