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Variable Basics

Variable Basics. Data Types & Printing. age. Variable. Symbol represents a place to store information name value memory space Example: somebody’s age An integer variable age; age = 20; Contrasted with constants No change in constants. Computer memory. 20. v1. v2. sum.

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Variable Basics

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  1. Variable Basics Data Types & Printing

  2. age Variable • Symbol represents a place to store information • name • value • memory space • Example: somebody’s age • An integer variable age; • age = 20; • Contrasted with constants • No change in constants Computer memory 20

  3. v1 v2 sum Why We Need Variables • Remember a value • Requests a value from the user • Results from calculation • Example: • int v1, v2, sum; • v1 = 50; • v2 = 30; • sum = v1 + v2; * = means assign the value as • Provide a way to access your computer's memory Computer memory 50 30 80

  4. Declaring • A variable must be declared before it can be used. • Tell the computer that you need to store a number in a variable • Mostly declared at the start of each function. • Declaration format: type name = initial_value; type name1 = initial_value1, name2 = initial_value2, …; • It is not required to put initial value in declaration

  5. Declaration of Variables type name = initial_value; type name1 = initial_value1, name2 = initial_value2, …; • { • int v1, v2, sum; • v1 = 50; • v2 = 30; • sum = v1 + v2; • } • { • int v1= 50, v2 = 30, sum; • sum = v1 + v2; • }

  6. Basic Types of Variables • int  • integer • float  • single-precision floating point • double • double-precision floating point • char  • one byte character • _Bool • Boolean

  7. Variable Names • Contain one or more characters, • A-Z, a-z • 0-9 • _ • Must start with a non-digit character • A-Z, a-z • _

  8. Variable Names – cont. • Cannot be C's keywords • int, main, while, etc • Limitation • Maximum of 63 characters for a variable name • Sometimes 31 • or 8 in very old C • Case sensitive: upper and lower case characters are different • floating • int • Int • main3 • 4yi Invalid Invalid

  9. int: integer Variables • For integral values only 10, -5, 1000 • no fraction 10.2 • no commas 12,000 • Ranges • Machine dependent • 32 bits (4 bytes) of storage on rain.cise.ufl.edu (usual) • Signed: −2,147,483,648 to +2,147,483,647 • Unsigned: 0 to +4,294,967,295 • Maybe 64 bits on others

  10. Print the value of an integer variable Display Integer Variables – I Preprocessor: interact with input/output of your computer #include <stdio.h> int main() Start point of the program { } Start and finish of function int value1, value2, sum; Declare Variables value1 = 50; value2 = 30; Define Values sum = value1 + value2; Summation printf(“The sum of 50 and 30 is %i\n“, sum); Printing results return 0; Finish and return value 0 The sum of 50 and 30 is 80

  11. Display Integer Variables – II #include <stdio.h> int main() { int value1, value2, sum; value1 = 50; value2 = 30; sum = value1 + value2; return 0; } printf(“The sum of %i and %i is %i\n“, value1, value2, sum); The sum of 50 and 30 is 80

  12. Number Bases • We are used to base 10: 0-9 • 42010 = 4 * 10 2 + 2 * 101 + 0 * 100 • Other bases • Hexadecimal (Base 16): 0-9, A-F • 42010 = 1 * 162 + 10 * 161 + 4 * 160 = 1A416 • Octal (Base 8): 0-7 • 42010 = 6 * 82 + 4 * 81 + 4 * 80 = 6448 • Binary (Base 2): 0-1 • 42010 = 1 1010 01002

  13. int: integer Variables – Special Case I Starting with digit “0” • Octal notation. Base 8, not 10 • 0,1,2,3,4,5,6,7 0177 = 1*64 + 7*8 + 7 = 127 0256 = ? • Display • %i – print out the decimal value • %o – print out the octal value • %#o – print out the octal value, starting with 0

  14. int: integer Variables – Special Case II Starting with digit “0x” • Hexadecimal notation. Based 16, not 10 • 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F 0x177 = 1*256 + 7*16 + 7 = 375 0xAF = ? 0x2AF = ? • Display • %i – print out the decimal value • %x – print out the hexadecimal value • %#x – print out the hexadecimal value, starting with 0

  15. Example - I #include <stdio.h> int main() { int a, b, c, d; a = 10; b = 20; c = 0177; d = 0xAF; printf(“The four numbers are %i, %i, %#o, %#x\n”, a, b, c, d); printf(“The four decimal numbers are %i, %i, %i, %i\n”, a, b, c, d); } The four numbers are 10, 20, 0177, 0xaf The four decimal numbers are 10, 20, 127, 175

  16. float: single-precision Variables • For values containing decimal 3., 125.8, -0.1 • Scientific notation 2.25e-3 = 2.25 * 10-3 = 0.00225 • Use e or E for exponent • No commas • Uses 4 bytes on *.cise.ufl.edu

  17. float Variables - II • Ranges • IEEE floating-point standard • e = 8, f = 23 • ±3.4×1038

  18. float Variables - III • Display • %f – print out the decimal value • %e – print out the scientific notation • %g – let printf decide the format • -4 < value of exponent < 5: %f format • Otherwise: %e format

  19. double: double-precision Variables • Similar to float • More storage space (IEEE floating-point standard) • float variables: e+f+1 = 32 • double variables: e+f+1 = 64 • Ranges • ±1.79769×10308 • Same display method as float • Operation similar as float

  20. char: character Variables • For single character • Enclosing the character within a pair of ‘ ’ • ‘a’ • ‘;’ • ‘P’ • ‘\n’ • ‘1’ • One Byte • Display • %c

  21. Example – II #include <stdio.h> int main() { int a, b, f; char c; a = 36; b = 52; c = ‘a’; printf(“The three numbers are %i , %i, %i\n”, a, b, c); printf(“The three characters are %c , %c, %c\n”, a, b, c); } ASCII TABLE The three numbers are 36 , 52, 97 The three characters are $ , 4, a

  22. _Bool: Boolean Type • For boolean • 0/1 • Normally means false/true • 1 Byte long • Display • %i

  23. Finish the Code #include <stdio.h> int main(void) { int integerVar = 100; float floatingVar = 331.79; double doubleVar = 8.44e+11; char charVar = ‘W’; _Bool boolVar = 0; printf(“integerVar = %? \n”, integerVar); printf(“floatingVar = %? \n”, floatingVar ); printf(“doubleVar = %? \n”, doubleVar ); printf(“doubleVar = %? \n”, doubleVar ); // scientific notation printf(“charVar = %? \n”, charVar ); printf(“boolVar = %? \n”, boolVar ); return 0; } %i %f %f %e %c %i

  24. Special variable types • short • usually use less space • add “h” after “%” in printf • long, long long • usually use more space • use “l” to indicate • add “l” after “%” in printf • signed, unsigned • specify whether is a signed quantity • use “u” to indicate unsigned • %u for unsigned

  25. Summary of Data Type

  26. Summary of Data Type – cont.

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