Beginning C for Engineers Fall 2005 Instructor: Bettina Schimanski TAs:Gabe Mulley & Joel Dever Website:schimb/beginC2005 Lecture 1 – Section

Beginning C for EngineersFall 2005

Instructor: Bettina SchimanskiTAs: Gabe Mulley & Joel Dever

Website: www.cs.rpi.edu/~schimb/beginC2005

Lecture 1 – Section 2 (8/31/05)Section 4 (9/1/05)

Beginning C for Engineers Fall 2005 - Lecture 1

Overview

Course Goals Introduction Unix and the History of C First C Program Data Types and expressions I/O


Course Goals Introduce general concepts of programming Begin to think like a programmer Start programming in C

Why is this important? To understand basic computer concepts To appreciate structured programming Will serve as a basis for any future programming

you do Needed for the Laboratory Introduction to

Embedded Control (LITEC) course – ENGR 2350


What is programming? Given a well-defined problem:

Find an algorithm to solve a problem Express that algorithm in a way that the computer can

execute it

An algorithm is a sequence of instructions to solve a problem such that: Each instruction is unambiguous and is something the

computer can do After an instruction is finished there is no ambiguity

about which instruction is to be executed next Execution finishes in a finite number of steps The description of the algorithm is finite


C Programming Language

Evolved from BCPL (1967) and B (1969) By Dennis Ritchie at Bell Labs

By the late 1970s it was widely used Standardized in 1989 in the US through the

American National Standards Institute (ANSI) and worldwide through International Standards Organization (ISO)

C++ is a superset of C


C Standard Library

C programs consist of many functions C Standard Library - collection of

existing functions

Programming in C is a combination of:Creating your own functionsUsing C Standard Library functions


C Portability

C is hardware-independentApplications in C can run with little or

no modifications on a wide range of computer systems

Use ANSI standard library functions instead of your own equivalent


RAM (memory)

I/O Devices

Central ProcessingUnit (CPU)

Secondary Storage

Registers

Computer

Architecture of a Computer

I/O devices Input Output

CPU ALU Main Memory Secondary Storage


I/O Devices Communications with the

outside world Input devices:

keyboard mouse joystick scanner microphone

Output devices: screen printer computer speakers networks

RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer


“Administrative” section of the computer – supervises operations: controls I/O and ALU

Has 2 components to execute program instructions

Arithmetic/Logic Unit performs arithmetic operations, and makes logical comparisons

Control Unit controls the order in which your program instructions are executed

Uses one or more registers as scratch space for storing numbers between instructions

A typical CPU today can execute millions of arithmetic operations in a second

RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer

Central Processing Unit (CPU)


RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer



RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer


Many computers now have multiple CPUs (multiprocessors) and can therefore perform many operations at a time


Main Memory

Sometimes called random access memory (RAM).

Stores the numbers (data) that a program uses when it runs on the computer.

Contains millions of circuits which are either off or on (0 or 1) Binary

Also stores the instructions of the program that is running on the computer.

Divided into fixed size units of memory called words. each word stores one

number each word has its

own address

RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer

Data

Program

Instructions


Main Memory

RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer

Data

Program

Instructions


Secondary Storage Permanent storage used to

save data and programs when they are not running on the computer.

Data and programs are organized into varying size units called files.

Files are organized into directories that can contain subdirectories.

Secondary storage is cheaper per Megabyte than main memory, but access to data is much slower

RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer


Secondary Storage

RAM (memory)

I/O Devices


Secondary Storage

Registers

Computer


The Programming Process Use an editor (such as Emacs, Notepad, Vi, etc.) to create a

program file (source file) contains the text of the program written in some programming

language (like C)

Use a preprocessor to include the contents of other files

Use a compiler to convert the source file into a machine code file (object file) convert from “English” to binary with machine operations

Use a linker to convert the object file into an executable file. include other machine code that the program requires

Run the executable file


Creating a C Program

A C program is a set of functions that collectively solve a given problem. each function is a sequence of C statements

(instructions) execution always begins with a function named

“main” one function calls another function to get it to execute

its statements

The C statements in a function are executed one after the other in sequential order as written. Each C statement is ended by a semi-colon.


First C Program Anything between /* and */ is a

comment intended to improve the readability of the program.

#include is used to tell the compiler and linker what library resources the program uses. the <stdio.h> library defines

everything you need to display messages on the screen

This program contains one function named “main”.

Notice where semi-colons are placed.

The program outputs (prints to the screen) the words

Hello, World!

/* Bettina Schimanski Hello World Program

prog01a.cAugust 31, 2005

*/

#include <stdio.h>

int main (){

printf(“Hello, World!\n”);

return 0;

}


Displaying Messages On The Screen: Using printf

To display a message on the computer screen use the printf statement.

The back slash “\” indicates an escape sequence. This means take the alternate meaning of whatever immediately follows it. \n means to start a new line \t is a tab \” is a quote \a is an audible alert (bell)

Text strings must always be surrounded by double quotes.

printf(“Hello, World\n”);


More Examplesprintf(“Hello\nWorld!\n”);printf(“\tFirst part of long message. ”);printf(“Second part of long message.\n”);printf(“\”Hello\” World!”\n”);

HelloWorld!

First part of long message. Second part of long message.“Hello” World!”


Defining a C Function

A C function has the following form:

The name of this function is “main”. The word “int” means that this function returns an integer number.

using 0 to indicate that the program ran correctly. this is what the return statement does at the end of the function

The braces define the beginning and the end of the function. The first line of the function is called the function header.

int main ( ){ sequence of statements separated by semicolons return 0;}


First Lab!

Go to

http://www.cs.rpi.edu/~schimb/beginC2005 Click on Lectures & Labs and go to Lab 1 Do just Part 1


Standard Data Types in C A data type tells what type of data is stored in a given

memory location. Standard C data types are broken into the following types:

Integral Types represent whole numbers and their negatives declared as int, short, or long

Floating Types represent real numbers with a decimal point declared as float, or double

Character Types represent single characters declared as char


C Variables

Variables in C store data in memory so that the data can be accessed throughout the execution of a program

A variable stores data corresponding to a specific type. Each variable that a C program uses must be declared at

the beginning of the function before it can be used. specify the type of the variable

• numeric types: int short long float double • character type: char

specify a name for the variable• any previously unused C identifier can be used (with some more

exceptions discussed later)

int x;

float sum, product;


What Does a Variable Declaration Do?

A declaration tells the compiler to allocate enough memory to hold a value of this data type, and to associate the identifier with this location.

int apartmentNumber;float tax_rate_Y2K;char middleInitial;

4 bytes for taxRateY2K 1 byte for middleInitial


Variable and function Names In C Some reserved

words in C:break case char const continue default do double else enum floatfor gotoif

int long returnshortsignedstaticstructswitchtypedefunionunsignedvoidwhile

Variables and function names in C are called identifiers. identifiers are used for many other

things as well Rules for constructing valid identifiers in C:

can contain letters (upper and lower case), digits, and the underscore ( _ ) character

cannot start with a digit cannot be a reserved word can be at most 256 characters long,

though some compilers only look at first 32 characters

are case sensitive


Identifiers VALID

apartment_number tax_rate_Y2K

PrintHeading ageOfHorse_

NOT VALID (Why?)

apartment# 2000TaxRate Age-Of-Cat day of week

** Using meaningful variable names is a good programming practice


Giving a Value to a Variable

You can assign (give) a value to a variable by using the assignment operator =

VARIABLE DECLARATIONSchar middleInitial ;char letter ;int apartmentNumber;

VALID ASSIGNMENT STATEMENTSmiddleInitial = ‘K’ ;letter = middleInitial ;apartmentNumber = 8 ;


Assignment Statement

An assignment statement is used to put a value into a variable. The previous value is replaced

Syntax:

<variable> = <expression>;

<variable> is any declared variable in the program <expression> is anything that produces a value of the

appropriate type (more on this later) first, the expression on right is evaluated. then the resulting value is stored in the memory location of

variable on left.


Examples:

count = 10;

count = count + 1;

area = 3.14 * radius * radius;

NOTE: An automatic type coercion occurs after evaluation but before the value is stored if the types differ for expression and variable

Examples


Arithmetic Expressions With Integers (int, long)

Operators: result is always an integer

Symbol Name Example Value (x = 10, y=3) + addition x + y 13 – subtraction x – y 7 * multiplication x * y 30 / quotient x / y 3 % remainder x % y 1 – unary minus –x -10 + unary plus +x 10


Arithmetic Expressions Continued…

You can string the operators together to build longer expressions. use parentheses to specify order of operations precedence (after sub-expressions in parentheses):

• first: unary plus and minus from right to left

• second: *and / and % from left to right• third: + and – from left to right


Arithmetic Expression Example

int y = 2; int z;z = -y * 3 * (4 + 5) % 10 + - -3;

-2 * 3 * 9 % 10 + - -3

-2 * 3 * 9 % 10 + 3

-6 * 9 % 10 + 3

-54 % 10 + 3

-4 + 3

-1


Arithmetic Expressions With Reals (float, double)

Arithmetic expressions with real numbers (numbers with decimal points) work the same way as with integers, with a few exceptions: there is no remainder operator (“%”) the “/” operator means “divide” (vs quotient), computing

the answer to many decimal places the result is a real value rather than an integer value

Important: Real values are approximate and may contain errors in the last few digits. about 7 digits of accuracy for type float about 14 digits of accuracy for type double


Mixed Mode Arithmetic Expressions

Arithmetic expressions: both integers and floats can get tricky. if both operands are integers, integer arithmetic is used if either operand is a float, float arithmetic is used

• an integer operand is converted to float for the operation

Examples:int a, x;x = 3.59; /* x gets the value 3 (no rounding) */float y = 3; /* y gets the value 3.0 */a = 12; /* a gets the value 12 */

float avg = (a + x) / 2; /* avg gets the value 7.0 … UH OH!!! */


Printing variables and constants to the screen with printf

• Use the following conversion specifications:%d for an integer %ld for a long integer %c for a character%f for a float %f for a double

Example: Output:

int sum = 5;float avg = 12.2;char ch = ‘A’;printf(“The sum is %d\n”, sum); The sum is 5printf(“avg = %f”\n”, avg); avg = 12.2prinf(“ch = %c\n”, ch); ch = Aprintf(“%d, %f, %c\n”, sum, avg, ch); 5, 12.2, Aprintf(“%d\n”, 5); 5

Note: see p. 153 in your textbook for a complete list of all data types


Reading data from the keyboard with scanf

Used to assign a value typed on the keyboard to a variable. Used similarly to printf. You must use the following conversion

specifications:

Data Type printf converstion spec. scanf conversion spec.int %d %dlong %ld %ldfloat %f %fdouble %f %lfchar %c %ccharacter string %s %s

The user must type a value followed by the Enter Key. Ex:

scanf(“%d”, &num);


Example: Program to find the average of two numbers

Note that you can declare more than one variable per line.

We divide by 2.0 instead of 2 so that the right hand side is a float (i.e. no truncation takes place)

scanf is used similarly to printf, except that you need to put an ampersand (&) before the variable name

The first argument of the scanf function is the conversion specifier(s) in quotes, then the variable name(s)

#include <stdio.h>

int main (){

int num1, num2;float avg;

/* get two inputs */printf( "Enter the first integer:”);scanf(“%d”, &num1);printf(“Enter the second integer:”);scanf(“%d”, &num2);

/* compute and print the avg */avg = (num1 + num2) / 2.0;printf(“The average is %f\n”, avg);

return 0;}


Finish Lab 1

Go to

http://www.cs.rpi.edu/~schimb/beginC2005 Click on Lectures & Labs and go to Lab 1 Do Part 2


Homework

Read Chapters 1,2 and 9 Due at the beginning of next class:

HW 1Academic Integrity Statement

FYI: Info on Cygwin, Putty, SecureCRT, and Emacs are on the website

Documents

Beginning C for Engineers Fall 2005 Instructor: Bettina Schimanski TAs:Gabe Mulley & Joel Dever Website:schimb/beginC2005 Lecture 1 – Section