Understanding Simple Data Types and Operators in C Programming

Chapter 2 Simple Data Types By C. Shing ITEC Dept Radford University

Objectives • Understand How to declare a variable • Describe C simple data types • Understand C expressions, operators and their priority level • Understand how to use format output (printf) • Understand how to use keyboard input: scanf • Understand how to design a small pogram

Variable Declaration • Declaration form: • Type identifier [= initial value]; Note: In ANSC C, you must declare all variables before using statements Identifier: • begins with a letter or underscore • Begins with underscore: for system • Begins with letter: for user • The rest either letter, digit or underscore • Up to 255 characters

Types • Simple data type • Modifier: (signed, unsigned), (long, short) except on char • char, int (default), float, double • Sizes are system dependent • int (16 or 32 bots), float (32 or 64 bits) • Use sizeof (type) operator to find the data type size • sizeof (char)=1<=sizeof (short)<=sizeof (int)<=sizeof (long) • sizeof (signed)=sizeof (unsigned)=sizeof (int) • sizeof (float) <= sizeof (double)<=sizeof (long double) • Structured data type • char[] (array, string), type * (pointer) • struct (record)

Simple Data Types

Initial Values • char: ‘A’, ‘\a’ (or ‘\7’,’\07’,’\007’ alert), ‘\\’, ‘\b’ (backspace), ‘\r’ (carriage return), ’\”’, ‘\f’ (form feed), ‘\t’, ‘\n’, ‘\0’ (null), ‘\’’, ‘\v’ (vertical tab), ‘\?’ • all characters are stored as ASCII integers • No constants of character type in C (However, yes in C++) • int: with or without sign • Decimal: -3 • Octal: 023 • Hexadecimal: 0x123

Initial Values (Cont.) • long: 1234567L • float: 0.123F • double: • Any number with decimal point is treated as double, e.g. 0.123 • Number in scientific notation, e.g. -123.45e-1

Expression • Combination of variables, constants and operators Example: x-1 > 5 is an expression

Operators • Increment and decrement: Prefix and postfix • ++, -- • Arithmetic • *, /, %, +, - • Relational • ==, !=, >, <, >=, <= (no space in between) • Logic • ! (not), && (and), || (or) • Conditional • Expr1 ? expr2 : expr3 • Comma (used in variable declaration)

Operators – Increment and Decrement • ++ variable/ -- variable • Increment(or decrement) variable by 1 before evaluating the current statement • variable ++/ variable – • Increment(or decrement) variable by 1 after evaluating the current statement

Operators - Arithmetic • / : quotient of 2 integers division Example: 5/9=0 9/5=1 Note: in order to get the desired result of 5/9, Use either one below: 5.0/9, 5/9.0. 5.0/9.0

Operators – Arithmetic (Cont.) • %: remainder of 2 integers division If negative integer is in exactly one of numerator or denominator, then do division as in all positive Numbers and just add a negative sign in front of the result. For example: (-40)/11=- (40/11)=-3 Note: Do not use negative numbers in % since it is implementation dependent.

Operators - Relational • Do not compare float or double number using == or != Example: double x=5.0; if (x == 5.0) { printf (“x=5.0\n”); // this line may not be //printed due to round off error }

Operators - Logic Example: int x=2; printf (“%d\n”, 1<x<3); // 1 is printed

Operators Priority

Example • Given a=2, b=-3, c=5, d=-7, e=11 (1) a/b/c= (2) 7+c* -- d/e = (3) 2* a%-b+c+1= (4) 7+ ++a%4=

Example • Given a=2, b=-3, c=5, d=-7, e=11 (1) a/b/c=(2/-3/5)=(-(2/3))/5=(-0)/5=-(0/5) =-0=0 (2) 7+c* -- d/e = 7+5*(-8)/11=7+(-40)/11 =7+(-(40/11))=7+(-3)=4 (3) 2* a%-b+c+1=2*2%3+5+1=4%3+5+1 =1+5+1=7 (4) 7+ ++a%4=7+3%4=7+3=10

Operators Exercises: Given int a=1,b=2,c=3,d=4; Find the values of the following table: Expression Value ________ _____ a*b/c a*b%c+1 ++a*b-c 7 - - b * ++ d a/b/c a/b % c 'A'+1 ('A'+1) < b a>b && c<d a< ! b || ! ! ‘A’ a + b < !c + c a - d || b*c && b/a

Operators Exercises: Answer Given int a=1,b=2,c=3,d=4; Find the values of the following table: Expression Value ________ _____ a*b/c 0 a*b%c+1 3 ++a*b-c 1 7 - - b * ++ d 17 a/b/c 0 a/b % c 0 'A'+1 66 ('A'+1) < b 0 a>b && c<d 0 a< ! b || ! ! ‘A’ 1 a + b < !c + c 0 a - d || b*c && b/a 1

Format Output - printf • Form: • printf(“%modifier format_code characters”, variables); Example: printf(“%6d\t%d\n”,number1, number2);

Format Output – printf (Cont.)

Format Output – printf (Cont.) • Modifier: printf(“%modifier format_code characters”, variables); • -: left justified • +: display + for positive, - for negative value • 0m: padded with leading 0s when less than m digits printed • n(integer): min number of spaces

Format Output – printf (Cont.) • Modifier : (Cont.) • p.q:min: • %f, %e, %E: • min total p spaces, q digits after decimal point • %g, %G: • min total p spaces, q significant digits • %s: • At least p total spaces, at most q spaces of the string • %d: • At least p spaces, min q digits displayed; padded with 0 if not enough digits • #: hexadecimal with 0x prefix • *.*: specify min spaces and # of digits after decimal point

Format Output – printf (Cont.) • Examples: • printf (“%s\n”, “How are you?”); • printf (“Beep me!%c\n”,’\a’); • printf (“A right-justified number: %6d”, 5); • printf (“A left-justified number: %-6d”, 5); • printf (“%6.2f\n”, 12.3F); • printf (“%*.*f\n”, 6, 2, 12.3F); • printf (“%6.2lf\n”, 1.236); • printf (“%#x\n”, 123); • printf(“%2.6d\n”, 123); • printf(“%2.4s\n”, “Morning”);

Format Output – printf (Cont.) • Examples: • printf (“%s\n”, “How are you?”); // How are you? Is printed • printf (“Beep me!%c\n”,’\a’); • printf (“A right-justified number: %6d”, 5); // 5 is printed • printf (“A left-justified number: %-6d”, 5); // 5 is printed • printf (“%6.2f\n”, 12.3F); // 12.30 is printed • printf (“%*.*f\n”, 6, 2, 12.3F); // similar to above • printf (“%6.2lf\n”, 1.236); // 1.24 is printed • printf (“%#x\n”, 123); // 0x7b is printed • printf(“%2.6d\n”, 123); //000123 is printed • printf(“%2.4s\n”, “Morning”); //Morn is printed

Format Output – printf (Cont.) • Examples: Hello World Example

Format Output – printf (Cont.) • Practice: Given int i=123; double x=0.123456789; Show what to be printed? statement print out ________ _______ printf("%d",i) printf("%05d",i) printf("%7o",i) printf("%-9X",i) printf("%-#9x",i) printf("%10.5f",x) printf("%-12.5e",x)

Format Output – printf (Answer) • Practice: Given int i=123; double x=0.123456789; Show what to be printed? statement print out ________ _______ printf("%d",i) 123 printf("%05d",i) 00123 printf("%7o",i) 0173 printf("%-9X",i) 0X7B printf("%-#9x",i) 0x7b printf("%10.5f",x) 0.12346 printf("%-12.5e",x) 1.23457e-01

Keyboard Input Format Function - scanf • Form: scanf(“format”, variable_address); • Format: similar to those used in printf Example: char c; int i; double db; scanf(“%c%d%lf”, &c, &i, &db); // sample data:a 100 -1.23 This is a sample data // c=‘a’, i=100, db=-1.23

Small Program Design • Comment: describe assumption, given input data, and output result. Write the algorithm how to achieve the output using the input • Define variables (use meaningful names and data types) that used to store input, output and intermediate results

Small Program Design (Cont.) • Input data: either store initial values in variables, get data from files or use keyboard input • Process data: use expression to calculate Results and store them in variables • Output result: display results in screen or store them in files

Small Program Design (Cont.) Example: /* Program Purpose: assumption: input: output: algorithm: Programmer’s Name: */

Small Program Design (Cont.) Example: (Cont.) int main(void) { double celsius, fahrenheit=…; // input celsius= …; // process printf (“…..”); // output return 0; }

Small Program Design (Cont.) • Example: Yard-Meter Conversion

Class Example • Example 1 • Example 2 • Example 3 • Example 4

Class Example (Cont.) • Use scanf function to read data from keyboard: Example 1 • Use redirect input (<) /output (>) from/to file: a.out < inputdata.txt > output.txt inputdata.txt output.txt • Use “for loop”: Example 1 • Interchange DOS and Unix format: dos2unix, unix2dos dos2unix dosformatfile.c unixformatfile.c

References • Herbert Schildt: C: The Complete Reference, 4th ed, Osborne Publishing • Deitel & Deitel: C How to Program, 4th ed., Chapter 2 & 9, Prentice Hall

Understanding Simple Data Types and Operators in C Programming