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Beginning Concepts for Problem Solving in C: variables, data types, operators, and formatted IO

BJ Furman

30JAN2010

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The Plan for Today

The concept of data Constants vs. variables Variables

naming rules data types

Operators and their precedence Practice writing and executing C programs

in ChIDE

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Learning ObjectivesFollowing completion of today’s lab, you should be able to:

List and explain the basic kinds of data Distinguish between variables and constants Declare integer, floating point, and character variables List the basic data types used in C Identify and explain commonly used operators in C Use C operators correctly according to their placement in the

hierarchy chart Write and execute simple C programs in ChIDE Set up and evaluate expressions and equations using variables,

constants, operators, and hierarchy of operations

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What and Why?

Data => pieces of information we deal with in the problem solving process

Why is it important to know about data types? Need to know about data types to effectively use a

programming language It’s all just bits the lowest level!

What would you rather work with…int i; float r;i = 3;r = cos(2*i*PI);

or…00000010 10000000 00000000 0000011010000010 10000000 01111111 1111110011001010 00000001 00000000 00000000

etc.

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Kinds of Data (simplified view)

The basic kinds of data that we will mostly use: Numeric

Integers: Real (floating point) numbers:

Character (are enclosed by single quotes in C) All letters, numbers, and special symbols

Ex. ‘A’, ‘+’, ‘5’

String (are enclosed by double quotes in C) Are combinations of more than one character

Ex. “programming”, “ME 30” Logical (also called ‘Boolean’ named after George Boole an English

mathematician from the early 1800’s) True or False (1 or 0)

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Kinds of Data - PracticeData Type

1. 17

2. “George”

3. 2.35

4. 0.0023

5. -25

6. ‘m’

7. 4.32E-6

8. “185.3”

9. 0

10. 1

If kind is ‘numeric’, then is it an integer or a floating point number?

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Constants and Variables Constant

A data element that never changes in your program 5, 62.37, 4.219E-6, “record_string”, ‘$’ i = j + 7; /* which one is the constant? */ first_letter = ‘a’; /* which one is the constant? */

Variable A data element that can take on different values

Its name represents a location (address) in memory i = j + 7; /* which are variables? */ second_letter = ‘b’; /* which is the variable? */

Values are ‘assigned’ using a single equal sign ( = ) Read the statement: i = j + 7;

NOTE!! Variables in C must be ‘declared’ before they can be used!

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Declaring Variables and Data Types

Variables must be declared before they can be used Gives info to the compiler about:

How many bytes of memory to set aside How to interpret the bytes (data)

Example: int my_var; /* an integer variable my_var */

float sensor1; /* a float variable sensor1 */

char Letter01_a; /* a char variable Letter01_a */ Two parts are needed in the declaration:

Data type designator (e.g., int), (note, a ‘reserved word’) Identifier (i.e., a name: my_var), must be a valid identifier

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Variable Names See the handout, ‘Notes on Variable Names’

Sequence of lower and/or upper case letters, digits, and underscores

Case sensitive! ex: my_num is not the same as My_num Initial character may not be a digit May not use reserved words as identifiers Keep length to 31 or fewer characters Make the first 8 characters unique Avoid names used by run-time libraries (e.g., log, which is used

in math.h) Avoid using names beginning with underscores Try to use lowercase letters for variable names, and UPPER

CASE letters for macro names (e.g., #define PI 3.14159) Choose names that are meaningful (e.g., light_level instead of

just output)

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Variable Naming - Practice

Variable Valid? Comments

1 bump_switch

2 sum1

3 sum3.2

4 num-var

5 NAME

6 register

7 1stname

8 lastname 2

9 _overflow

10 signal

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Data Types and Memory Recall that declaring a variable

sets aside memory and indicates the type of data that will be stored

Considerations in declarations What kind of data will you be working with?

Just whole numbers? Fractions? Characters? Is speed important?

Integer operations are fastest How much memory is available?

Important for embedded systems and microcontrollers What is the range of the data?

From 0 to n, or from –n to +n, etc. What kind of precision do you need?

Precision number of decimal places

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Data Types

enumArithmetic TypesPointers

Aggregate TypesScalar Typesvoid

Integral Types Floating Types

arrays structs unions

unsigned signed

charshortintlonglong long

floatdoublelong double

Hierarchy of Data Types

(adapted from Darnell, P. A. & Margolis, P. E. (1996) C, a software engineering approach, 3rd ed., Springer, New York.)

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Memory Allocation for Arithmetic Data Types

Size (bytes) Range of Values

Name (alternate) Description AVR GCC MSVC++ AVR GCC MSVC++

char Character or small integer 1 1Signed: -128 to 127 (-2(8-1) to 2(8-1)-1)Unsigned: 0 to 255 (0 to 28-1)

Signed: -128 to 127Unsigned: 0 to 255

short int (short) Short integer 2 2Signed: -32768 to 32767Unsigned: 0 to 65535

Signed: -32,768 to 32,767Unsigned: 0 to 65535

int Integer 2 4Signed: -32768 to 32767Unsigned: 0 to 65535

Signed: -2,147,483,648 to 2,147,483,647Unsigned: 0 to 4,294,967,295

long int (long) Long integer 4 4

Signed: -2,147,483,648 to 2,147,483,647

Unsigned: 0 to 4,294,967,295

Signed: -2,147,483,648 to 2,147,483,647Unsigned: 0 to 4,294,967,295

long long int (long long) Really long integer 8 8Signed: -9.2E+18 to 9.2E+18Unsigned: 0 to 1.8E+19

Signed: -9.2E+18 to 9.2E+18Unsigned: 0 to 1.8E+19

float 'Single-precision' floating point number 4 4 1E 38 (7 decimal digits of

precision) 1E 38 (7 decimal digits of precision)

double 'Double-precision' floating point number 4 8 1E 38 (7 decimal digits of precision)

1E 308 (15 decimal digits of precision)

long doubleLong double-precision floating point number 8

1E 308 (15 decimal digits of precision)

(See the handout, “Notes on Data Types”)

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Declaration Practice

Declare the following variables: A character variable named PORTA that will hold

only non-negative numbers A variable named up_down that will hold whole

numbers ranging from -20,000 to 20,000 A variable named heat that will hold values from

-20.0 to 350.0 A variable named max_read that needs 8 decimal

digits of precision

For each variable declared, comment on the number of bytes of memory needed and the data range it will cover

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Operators

Operator: a symbol (or combination of symbols) used to combine variables and constants to produce a value(Overland, B. (1995) C in plain English, MIS Press, New York.)

The variables and constants that get combined are called ‘operands’

How the combining is carried out depends on the precedence and associativity of the operator

Example – identify the operator(s), operands, and results on each line:int i, j = 3;i = j + 7;

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Operator Precedenceand Associativity

• All operators have the properties of precedence and associativity.

• Precedence has to do with which operations take priority in groupings of operands around adjacent operators

• Associativity has to do with which operations take priority when the operators in an expression have the same precedence

• Use parentheses () to specify a particular grouping order and to make expressions more readable

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Operator Practice

Identify the operators, operands, and results on each line

int i, count, mult, mult2=1, total_sum;

float total_percentage; i = 1;mult = total_sum = i;count = i + 1;count = count + 1;total_percentage = total_sum / 100; /* a little tricky! */mult1 = count * 17.23;count += 1;mult2 *= 2;

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Arithmetic with Mixed Data Types

Fundamentally, the computer is not able to arithmetically combine data of different types Arithmetic with integers integer results

int div_int = 8 / 5; /* what is div_int? */

Arithmetic with floating point data floating point results

float div_flt = 8.0 / 5.0; /* what is div_flt? */

Arithmetic with integers and floating point values in the same expressions ??

int div_int = 8.0 / 5; /* what is div_int? */ float div_flt = 8.0 / 5; /* what is div_flt? */

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Implicit Type Casting

In binary operations (e.g., +, -, /, etc.) with operands of mixed data types, the resultant data type will take the higher order data type of the two operands1

1Cheng, Harry H. (2010). C for Engineers and Scientists: An Interpretive Approach, McGraw-Hill, New York.

long double

double

float

unsigned long long

long long

unsigned long

long

unsigned int

int

unsigned short

short

unsigned char

char

Higher

Lower

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Expressions and Statements

Expression Any combination of operators, numbers, and names

that evaluates to a single value 5 j = 17 j = i = 10 i + j

Statement A chunk of code that does something (executes)

Terminating an expression with a semicolon (;) turns it into a statement

We will cover other statements later

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Getting Started with Ch and ChIDE

BJ Furman

11JUL2009

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What is Ch? an embeddable C/C++ interpreter for cross-

platform scripting, shell programming, 2D/3D plotting, numerical computing, and embedded scripting Developed by Prof. H. Cheng at UC Davis Interpreter vs. compiler

Executes expressions and statements immediately rather than having to construct a complete program and go through compile/link/execute/debug cycles

Superset of C Supports all features of ISO 1990 C Standard (C90) and

major features of C99 Lots more features!

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More Information on Ch

See The Ch Language Environment, ver. 6.1 User’s Guide Available from: http://www.softintegration.com

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Starting up Ch

Ch command shell and ChIDE Ch command shell can be invoked

from the Ch icon Can interactively execute C programs,

functions, statements, and expressions

ChIDE can be invoked from the ChIDE icon Can easily access the Ch command shell

from within ChIDE Can easily invoke a 3rd party compiler (e.g.,

MS Visual C++ Express)

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Ch command shell

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ChIDE Click on the Ch icon to launch a Ch shell window

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Laboratory Exercises Work individually unless not enough computers

Take turns at the keyboard if you have to work with a partner Open ChIDE and launch a Ch shell window Open a new window in ChIDE

File | New or Ctrl-N Follow the instructions on the

Lab Project #1 guide sheet Fill out the worksheets Complete the cover page Description is especially important

In your own words, not plagiarized

Save your work on a personal storage device before you leave

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Formatted Output

BJ Furman

16JUL2009

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Formatted Output

We use the printf function (stands for ‘print-formatted) to display text and numeric information to the screen printf is available by including the Standard IO

library, stdio.h (more on this later) Ch already “knows” about printf, so it is not

necessary to include stdio.h

Ex. Print a line of textprintf("Hello ME 30!!");

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printf() – a closer look General form:

printf(“control string”, arg1, arg2,…); Control string

A string enclosed in double quotes that controls the conversion and formatting of zero or more arguments

Arguments are expressions that the function printf acts on Inside the control string will often be conversion specifications

and modifiers that specify how the data from the arguments is to be converted into displayable form

Escape sequences (a \ followed by a letter or combination of digits)) are also used to control the position of the cursor and/or provide literal representations of non-printing or special characters

Ex. Try this in ChIDE

printf("printf example:\n 1+1=%d\n", 1+1);

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Conversion Specifications (partial list)

ConversionSpecification

Output

%ccharacter (if datum is an int, prints ASCII value corresponding to least significant byte)

%s string of characters

%d or %i decimal integer

%e, E floating point number in e (or E)–notation

%f floating point number (float or double) in decimal notation

%g, Guses %f or %e, E depending on datum value. Trailing zeros are removed

%u unsigned decimal integer

%o octal integer (base 8)

%x, X hexadecimal integer (base 16), lower, Upper case

%% Prints a % sign

Adapted from: http://www.eecs.umich.edu/~bartlett/printf.html

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Escape Sequences (partial list)

EscapeSequence

Represents

\a Bell (alert)

\b Backspace

\f Formfeed

\n New line

\r Carriage return

\t Horizontal tab

\v Vertical tab

\' Single quotation mark

\“ Double quotation mark

\\ Backslash

\? Literal question mark

http://msdn.microsoft.com/en-us/library/h21280bw(VS.80).aspx

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Conversion Specification Flags Optional format modifiers that may come before

the conversion character (Darnell & Margolis, 1996)

Flag Meaning

- Left justify

+ Prefix numeric data with a + or – sign. Takes precedence over a blank space if both are given

space Causes negative numbers to be prefixed with a – sign and positive numbers with a space (default is no space for positive numbers)

# No effect for c, d, I, s, and u specifiers. For o, printed value will be prefixed with a zero. For x and X, prefixes value with 0x or 0X. For e, E, f, g, and G, causes results to contain a decimal point, even if precision is zero. For g and G, trailing zeros will not be removed from results as they normally are.

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Field Width Specification

Optional specification of minimum number of characters to output Will pad to the right or left to fill specified

width if data requires fewer characters Default is pad on the left (i.e., RIGHT justify), but

can specify right pad (i.e., LEFT justify) with the left adjustment flag (the minus sign)

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Precision Specification

Signified by a period followed by a decimal constant (e.g., %5.2f) Floating point values

Specifies the number of digits to appear after the decimal point

Will round if actual value exceeds the specified precision

Integer values Same meaning as field width specifier, but

overrides it. Will pad the field with zeros on the left until the precision length is reached

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Short and Long Specifiers

Specifier Meaning

h Corresponding data item is a short int or unsigned short int

l Corresponding data item is a long int or unsigned long int

L Corresponding data item is a long double

Data conversions take place when arguments are passed to the printf function Integers are converted to int Floating point to double

To ensure arguments are cast back to their original types, use short and long specifiers

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Practice - operator precedence

On paper, determine output of:

int i, j = 3;i = j + 7;i = j / 12 + 5; int k = (j + i * 3); printf(“%d, %d, %d”, i, j, k);

Output:

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Practice - operator precedence solution

Program Trace:

int i, j = 3; /* j = 3 */

i = j + 7; /* i = 3+7 = 10 */

i = j / 12 + 5; /* i = (3/12)+5 = 9 */

int k = (j + i * 3); /* k=3+27=30 */

printf(“%d, %d, %d”, i, j, k);

Output: 9, 3, 30

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Formatted input

BJ Furman

18JUL2009

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scanf() function (just a brief treatment!)

scanf() is like the reverse of printf It reads data entered via the keyboard Similarities to printf():

Needs a format string first Many common format specifiers, which indicate the type of

data expected from the keyboard Which must match the data arguments

Any number of data arguments Differences from printf():

Data argument identifiers must be preceded with an ampersand (&)

The & ahead of the variable signifies the address in memory where the data will be stored (its a pointer to the variable)

Beware!!! Forgetting the & is a common error.

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scanf() function, cont. Differences from printf(), cont.:

Characters other than a conversion string, a space, a newline character, or a vertical tab must match characters in the input stream

A space, horizontal tab, or newline character in the format string causes scanf() to skip over leading white space up to the next nonspace character

scanf(“Distance= %lf", &num1); Will skip leading spaces before the value num1 Must find a match to the string literal, Distance= (or else

it will stop reading the input and will return the number of successful conversions that were stored (try entering a space before typing Distance=)

Darnell & Margolis (1996)

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scanf example 1

Prompt the user for a integer, and store it in an integer variable named num1

int num1;

printf("Enter an integer > ");

scanf("%d", &num1);

printf("The value you entered is %d\n", num1);

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scanf example 2

Prompt the user for a floating point value, and store it in an floating point variable of type double named dbl_num2

double dbl_num2;

printf("Enter a floating point number > ");

scanf("%lf", &dbl_num2);

printf("The value you entered is %G\n", dbl_num2);

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Anatomy of a C program

BJ Furman

18JUL2009

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Structured Programming

A formal letter has a structure So does a program in C

Burford FurmanProfessorDept. of Mech. and Aero. EngSan José State UniversitySan Jose, CA 95192-0087

July 20, 2009

Dear Prof. Furman,

I’m writing you to see if I can get into ME 30……

Sincerely,

Jane Student

Title block

Date

Salutation

Body

Closing

Signature

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Essential Program Structure

/* Programmer’s Block */ Description and documentation of the program#include directives Compiler instructions to access to a library#define directives Compiler instructions for replacement macroglobal variable declarations Declaration of variables with global scopeglobal function declarations Declaration of functions with global scopeint main() Calling of the function ‘main’{

variable declarations Declaration of variables with local scope function declarations Declaration of functions with local scopevariable initializations Initialization of local variablesstatements Statements forming the core of the programreturn 0; Value to return when main() completes

}/* function definitions */function name(parameter list) Header of function (i.e., name and parameters){

statements Statements forming the core of the function}

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A C program (Fig. 2.1 in H&K, p. 47)

/* Converts distances from miles to kilometers. */

#include <stdio.h> /* printf, scanf definitions */

#define KMS_PER_MILE 1.609 /* conversion constant */

int main(void) {

double miles, kms; /* miles->dist. in miles, kms-> equiv. distance in kms */

/* Get the distance in miles. */printf("Enter the distance in miles> ");scanf(“%lf", &miles);

/* Convert the distance to kilometers. */kms = KMS_PER_MILE * miles;

/* Display the distance in kilometers. */printf("That equals %f kilometers.\n", kms);

return (0);}

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A C program Annotated (Fig. 2.1 in H&K, p. 47)

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References

Darnell, P. A. & Margolis, P. E. (1996) C, a software engineering approach, 3rd ed., Springer, New York.

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Extra Items

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Memory Stores program instructions and

data Memory (8-bit)Address

0 1 1 0 0 1 1 0

0 1 0 1 0 1 0 0

0 0 0 0 0 0 0 0

0x10FE

0x10FF

0x1100

0xFFFF

Bit 7 6 5 4 3 2 1 0

Each location hasan ‘address’

Each location storesthe information as ‘bits’ Binary ____its

Zero or one

8 bits is one byte Information is ‘coded’ Memory is ‘written’ or ‘read’

Back

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Hierarchy of Data Types

Back

(adapted from Darnell, P. A. & Margolis, P. E. (1996) C, a software engineering approach, 3rd ed., Springer, New York.)

Data Types

enumArithmetic TypesPointers

Aggregate TypesScalar Typesvoid

Integral Types Floating Types

arrays structs unions

unsigned signed

charshortintlonglong long

floatdoublelong double

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Reserved Words in C

auto double int struct

break else long switch

case enum register typedef

char extern return union

const float short unsigned

continue for signed void

default goto sizeof volatile

do if static while

You may not use these as variable names

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