CSC 215

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CSC 215 Introduction to Structured Programming
with C Instructor Eric Sedgwick
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Administrative Issues

• Roll Call
• Syllabus
• WebPage
• HyperNews
• Lab

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Tonight

• Class administration
• Introduction to C programming

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Are you in the right class?

• This course is a prerequisite for CSC 310. You
  should not be taking both at the same time!
• CSC 225 - for those with programming experience
• Java

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CSC 215 covers

• Intro to programming
• variables and types
• looping
• branching
• functions
• call by reference
• call by value

• file I/O (input/output)
• arrays
• strings
• and, hopefully
• classes
• recursion

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Q What is the purpose of CS 215?

• A1 To learn the syntax (grammatical rules) of
  C.
• A2 To learn how to program. This is harder, and
  more important.

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C

• Created by Bjarne Stroustrup, ATT, 80s
• Extends C, most C programs are C programs
• A high-level language
• A compiled language
• Supports object-oriented programming (covered in
  CS310)
• Widely Used

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Programming

Problem Statement
Algorithm(Recipe)
?
Program
A problem well stated is a problem half solved
-Charles Kettering, inventor of the electric
cash register
Experiment !
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Algorithm

• An algorithm is a sequence of precise
  instructions that leads to a solution.
• Recipe

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C Compiler
Object Code(executable on computer)
Source Code(entered by programmer)

• Translates from high-level code (C) to
  low-level code (object code) that can be
  understood by the machine.
• Microsoft Visual C is available in the labs and
  is the recommended compiler.
• Linking - combine with previously compiled code
  (for example input/output code)

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hello.cpp

• Type into editor
• Compile\Link\Execute
• To save output - cut and paste
• Save source code ( .cpp) to diskette
• Turn in
• Hard Copy of source code and output

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Using Visual C

• Create folder (directory) for your files on hard
  drive
• Create source file
• File gt New gt files gt C source file gt type name
• Build compile and link
• respond yes to create default workspace?
• Important close workspace before creating a new
  file
• In lab copy source files to your floppy disk

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peas.cpp

• Copy from disk to hard drive
• Errors
• Syntax Error, program compiles with erroror
  warning
• Logic Error, program does the wrong thing
• Run-Time Error, e.g., division by zero

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Layout of a simple program

• include ltiostreamgt
• using namespace std
• int main() Variable Declarations Statement_
  1
• Statement_2 Statement_n return 0

Necessary for input and output
Every program has exactly one main function
Statements are the instructions thatget executed
Signal that program terminated sucessfully
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Syntax

• include ltiostreamgtusing namespace std
• include directive and namespace
• necessary for input and output
• cin gtgt
• reads from the keyboard
• cout ltlt
• outputs to the screen
• \n
• newline character

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Programming Goals

• Eliminate errors
• Syntax - error or warning when compiling
• Logic - program does the wrong thing
• Run-Time - e.g., division by zero,
• Style
• Program should be easy to read and understand.

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Execute code by hand

• Important skill
• read code and determine the output
• usually need pencil and paper
• The two most important types of questions on the
  exams
• write code to perform task
• execute code by hand

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bars.cpp

• What does this program do?
• What happens if the user inputs the numbers
• 3
• 2.3
• 7
• 1.1
• Variables
• Input and Output

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Comments

• Comments are ignored by the compiler, and are
  used to provide information to people (the
  grader) reading your source code. There are two
  forms.
• Everything on the line following // is ignored.
• // bars.cpp
• // author Eric Sedgwick
• double height // in centimeters
• Everything between / and / is ignored
• /
• This program was last modified 9/13/99
• /

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Variables
memory

• A variable is a box in which to store values.
• Actually an allocated block of memory.
• The value of a variable can be changed repeatedly
  
• Every variable has a type ...integer number,
  floating point number, character, word, ...
• The name of a variable is called an identifier.

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Identifiers

• Start with _ or letter
• Other characters are either _ , letter, or
  digit
• Cannot use reserved words (keywords)
• return, int, double, ...
• Do not use names that already used.
• main, cout, cin, ...
• Legal x, a123, f_1, Rate, count, _number_
• Illegal 123a, g.h, this_at_here

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More on Identifiers

• C is case sensitiveCount, COUNT, count, CoUnT
  are all different identifiers.
• Choose meaningful names
• interest_rate is better than x
• Caution! some compilers do not use all characters
  of the identifier. (Can assume 6 are used.)
• interest_rate1 vs. interest_rate2
• what about your compiler?

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Variable Declarations
memory

• Variables must be declared before they can be
  used. This allocates space in memory. The amount
  of space depends on the variable type.
• Bit - a binary digit - 0 or 1
• byte - 8 bits
• Form of a Declarationtype_name
  variable_1,variable_2,
• Examplesint soc_sec_numdouble
  degrees,wind_chill

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Types

• int - integer 5 423,564 -97,234
  0
• double - floating point number 5.1 0.0
  -4.2 0.0023 1.5e03
• More types soon!
• bool, long double, char, float

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Assignment Statements
memory

• To change the value of a variable use an
  assignment statement.variable expression
• Examplesdistance speed timeinterest_rate
  prime_rateanswer -13count count 1

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What is the output?
memory

• ... double interest_rate, prime_rate
• interest_rate prime_rate 5.9
• cout ltlt interest_rate
• ...

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Variable Initialization

• Initializing Declaration
• type_name variable_1 expression_1, variable_2
  expression_2, variable_n
  expression_n
• Exampledouble interest_rate, prime_rate 5.9
• A very good idea!
• Be careful with initialization and loops!

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I/O - Input and Output

• Need to get data to the program.
• We will work with I/O streams
• cin - input stream associated with keyboard
• cout - output stream associated with terminal
• Later we will learn how to work with files.

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Output using cout

• bars.cpp
• To insert spaces between numbers
• cout ltlt number_1 ltlt ltlt number_2
• For a new line
• \n is used inside quotes
• cout ltlt number_1 ltlt \n ltlt number_2
• endl is used without quotes
• cout ltlt number_1 ltlt endl ltlt number_2
• For mathematical expressions use parentheses
• cout ltlt The sum is ltlt (number_1 number_2)

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Decimal Points

• What is the output?
• double price 75.5
• cout ltlt The price is ltlt price ltlt endl
• Depending on the compiler
• The price is 75.5000 -or-
• The price is 75.5 -or-
• The price is 7.55000001

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• Use magic formula
• double price 75.5
• cout.setf(iosfixed)
• cout.setf(iosshowpoint)
• cout.precision(2)
• cout ltlt The price is ltlt price ltlt endl
• Output
• The price is 75.50
• For other precisions
• cout.precision(?)

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cin

• More than one variable can be read by a single
  statement.
• cout ltlt Please enter month day year. \n
• cin gtgt month gtgt day gtgt year
• Numbers can be separated by some number of
  whitespaces (spaces, tabs or newlines). Either
  of these are ok
• Please enter month day year. Please enter month
  day year.
• 10 13 1999 10 13
• 1999

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cout and Escape sequences

• Escape sequences
• \n - newline character
• \t - tab character - useful for lining up tables
• \a - alert
• \ - double quote
• \\ - backslash
• Each is a single character!

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weight.cpp

• Design an algorithm, then write a program (on
  paper) that allows the user to input a weight in
  kilograms, converts it to pounds, and then
  outputs the answer. For our purposes, each
  kilogram weighs 2.204 pounds.

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I/O Goals

• Prompt user on what to enter.
• Echo input back to the terminal, so that the user
  knows that the information was inputted
  correctly.
• Provide text so that the user knows what the
  output means. Dont just output numbers.
• End your programs output with a new line.

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HW

• First Assignment is posted and due in a week!
• Submit via email
• attach source files (.cpp files) to email
• CSC215HW