C++ BasicsC++ BasicsCS 1428 Week 2

Texas State UniversityTom O’HaraSpring 2011

Important topics from week Important topics from week 11Basic computer organization

◦von Neumann architecture◦CPU, registers, memory, etc.

Algorithm versus program◦Top-down stepwise refinement◦Program syntax

C versus C++

Lecture OverviewLecture OverviewC++ program structurePreprocessorData types overviewConstantsVariablesData type detailsC++ Gotcha’s

Common Program Common Program StructureStructure

Program header

Main function:

Start of block

Declarations

Input

Processing

Output

Exit code

End of block

#include <iostream>

using namespace std;

int main ()

{

double celsius, fahrenheit;

cin >> celsius:

fahrenheit = 9.0/5*celsius+32;

cout << fahrenheit;

return (0);

}

Skeleton ProgramsSkeleton ProgramsTemplates with “fill in the blanks”Useful for simple programsAvoids compilation errors due to

typo’s◦#'s, <'s, etc. wreak havoc on poor

typists!Customize yourself on ongoing basis

◦Add name, email alias, etc.◦Revise based on code typed over and

over again

Sample C++ Program Sample C++ Program SkeletonSkeleton

// <program description goes here>

#include <cstdlib> // Common routines like system

#include <iostream> // I/O streams cout & cin

using namespace std; // Import standard namespace

int main ()

{

<variable declarations and initializations go here>

<program statements go here>

// Exit with successful execution statussystem("PAUSE"); // wait for user (for Dev C+

+)return (0);

}

PreprocessingPreprocessingInclusion Files (“header files”)

◦Tells compiler which library packages required

#include <iostream>FYI: Text substitutions

◦Poor man's symbolic constants#define PI 3.14159

◦Efficient alternative to functions#define MAX(x,y) (x > y ? x : y)

◦Not recommended (esp. for beginners)! C++ has good alternatives to each of these

Data typesData typesIn memory, data is all the same: 1's

& 0'sLanguages provide common

abstractions◦Numeric

integers {..., -2, -1, 0, 1, 2, ...}

real numbers (e.g., 3.15159, 6.022x1023)

◦Textual (single) characters {'A', 'B', 'C', ...}

strings (e.g., “home address", "C++")

C++ Constants (aka C++ Constants (aka literals)literals)Values that never changeIntegers: [sign]digit...

7 13 -1 +100000

Reals: [sign]digit...[point]digit...[e[sign]digit...]

-7.0 1e9 0.5 6.022e23 -1.75e-50

Characters: 'character''A' 'b' ''©'' ' '

Strings: "character...""San Marcos, TX" "Jane Doe" ""

Syntax NotationSyntax Notation◦category italicized text indicates a type

digit one of {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}◦text boldface text must be specified as is

if the keyword 'if' (used in decisions)◦x | y a choice between item x or y

+|- numeric sign (i.e., a plus or minus)◦[specification] brackets indicate optional items

[+|-] an optional plus or minus sign◦ item ... one or more instances of item

digit... a series of digits

VariablesVariablesVariables hold values that can changeSymbolic names for memory location

“average” in place of “@1123”

Declaration: type label [= value];

char initial = 'P';

Labels use alphanumeric characters and '_'

alpha [alpha | numeric | _]...

total pi standard_deviation Boeing747

Character dataCharacter dataSingle character

◦1 byte (8 bits, so 28 or 256 distinct values)◦Any of the ASCII characters from Appendix B

char grade = 'A'; // underlying value is code 65

Character strings◦Unlimited:1byte per character + 1 for end mark

string pet = "dog"; // values: 100, 111, 103, 0char* name = "O'Hara"; // old way ("C string")

Escape sequences for special characters\t \n \0 \\ // tab, newline, null and backslash

Numeric dataNumeric dataIntegers

◦int data type◦Usually 4 bytes (32 bits;, so > 4 billion values)◦int num_students = 40;

Floating◦double data type◦Usually 8 bytes (64 bits, so > 1.8x1019 values)◦The ‘float’ type just uses 4 bytes but

uncommon◦double average_temp = 94.5;

Logical dataLogical dataBoolean values (i.e., true or false)

◦bool data type◦Value false is 0, and value true is 1◦Usually 1 byte

For making programs more readablebool needs_payment = true;if (age < 18) needs_payment = false;if (age < 65) needs_payment = false;…if (needs_payment) cout << "Payment

required";

Basic arithmetic operatorsBasic arithmetic operatorsAddition and subtraction

expr1 + expr2 num_undergrads + num_grads

expr1 - expr2 num_students - num_failures

Multiplication and division expr1 * expr2 2 * pi * radius expr1 / expr2 width / 2

Modulus (aka remainder) expr1 % expr2 count % 2

C++ Gotcha'sC++ Gotcha'sInteger versus floating point division

F = 9/5 * C + 32 => 9.0/5.0 * C + 32

Treating numbers as strings and vice versaint course = "1428"; int course = 1428;

string bond = 007; string bond = "007";

Single versus double quotes◦Characters use ', but strings use "◦Use escapes for embedded quotes: '\"' "\'"

FYI: Scope of identifiers within blocksif (x > 10) { int y = 5; … cout << y; } // y visiblecout << y; // compiler error: y only occurs in if-block

FYI: Special case data typesFYI: Special case data typesUnsigned int’s (and also char’s)

◦The unsigned qualifier doubles the maximum:

[-231, 231-1] [0, 232-1]

The sign is omitted, so range change from

[-2147483648, 2147483647] to [0, 4294967295]

The long and short qualifiers◦For extra/reduced capacity integer (or floats)◦Platform-specific and uncommon these days

Not important for this class

Program CommentsProgram CommentsFormat: // arbitrary-text Describes intention of program segments

// Interchange values of x and yx = y;y = x;

Myth of self-documenting programsThe above segment is actually incorrect, which might not be apparent without the comment.

Comment in groups, not every statement

Making programs readableMaking programs readablePlace comments throughout

◦Top of program◦Before each function

Except main in simple programs (as top suffices)

Use descriptive variable names◦ex: Use 'temperature' rather than t

Use ample whitespace◦Blank line before comments◦Several before function definitions (e.g.,

main)

Simple OutputSimple Outputcout output stream

◦<< operator◦Format: cout [<< value]… ;

Examples◦cout << "Enter the patient's name: ";◦cout << "The temperature is " << temp;

Gotcha's◦The << must be repeated (commas not

allowed)◦endl required for end of line (or "\n")

cout << "The height is " << height << endl;

Preview: Simple InputPreview: Simple Inputcin input stream

◦<< operator◦Format: cin >> variable [>>

variable]... ;Example

cin >> patient_name;Gotcha's

◦Decimals ignored if integer type◦Whitespace terminates input for strings

Covered next week (chapter 3)

Chapter 2 SynopsisChapter 2 SynopsisImportant

◦Sections 1, 4, 6, 7, 8, 13Useful

◦Sections 2, 3, 5, 9, 11Marginal

◦Sections 10, 12, 16◦Tables 2-2 (keywords), 2-6 (misc.

integer types)◦Serendipity project (likewise in other

chapters)

C++ ResourcesC++ ResourcesOnline reference manuals

www.cplusplus.comwww.cppreference.com

PDF Reference Manualhttp://www.ibm.com/support/docview.wss?uid=swg27002103

Bjarne Stroustrup’s web page on C++http://www2.research.att.com/~bs/C++.html

Humorhttp://www.softpanorama.org/Lang/Cpp_rama/

humor.shtml

Example: "C++: Hard to learn and built to stay that way."