02 c Cpp Differences

8/6/2019 02 c Cpp Differences

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C vs C++Chapter 1



Review of C/C++: Variables

Several different types

int integers (2, 7, 12)

float decimal numbers (3.14, 7.81)

char single characters (µa¶, µ4¶)

char[] used for strings (³Hello´, ³Hi´)

bool true or false

int a = 5;

char name[] = ³Compton´;

float f = 42.123;

C++ only!



Control Structur es (if-then-else)

if (condition1) {...

} else if (condition2) {...

} else {

..

.}

if (a < b ) {c = a;

} else if (b < a) {c = b;

} else {

c = d;}



Control Structur es (while/do-while)

while (condition1) {

.

.

.

}

do {

.

.

.

} while (condition2);

while (x > 0) {

x--;

}

do {

x--;

} while (x > 0);



Control Structur es (for )

for (x = initial value; condition; iteration) {

.

.

.

}

for (int x = 0; x < N; x++) {

A[x] = x;

}



Control Structur es (switch)

switch (expression) {case value1:

.

.

.

break;case value2:

.

.

.

break;default:...

}

switch (letter) {case µa¶:

a++; break;

case µb¶:

b++; break;

case µc¶:c++;

break;

default:}



Arrays

int values[4] = {5, 8, 2, 0};

char name[8] =

{µC¶, µo¶, µm¶, µp¶, µt¶, µo¶, µn¶, µ\0¶};

Group homogenous information together

REMEMBER WE START COUNTING AT 0! int v[4] means we actually have 4 elements:

v[0], v[1], v[2], and v[3].

There is no v[4]!



I/O

x = 5; printf(³Hello. x = %d\n´, x);

int i; printf(³Enter a number: ³);scanf(³%d´, &i);

In C, we used printf() and scanf()

In C++, we use cout and cin

Many ways to format strings for cout

More on using these modifiers later

.Net and C# go

back to this

somewhat



Functions

int average(int n1, int n2) {

return (n1+n2)/2;

}

int main() {

int a = 5;

int b = 6;

printf(³The average of a and b is: %d\n´,

average(a, b));

return 0;

}

Formal parametersC++

Actual parameters

(arguments)



struct Essentially a collection of variables

Used when heterogenous information needs to be

grouped

Can have arrays of structs (orthogonality)

By default, everything¶s public

Functions allowed within structs in C++ (class is astruct on steroids

struct ComputerCourse {int id;int nStudents;

};

int main() {ComputerCourse course;course.nstudents = 15;course.id = 322;

}



Pointers

int x = 10;

int * y = &x;

*y = 20;

Special variable that only holds memory addresses Holds the location (address) of information, not the

information itself

Two operators: address-of and dereferencing operators

&v ariable ³the address of variable´

* pointer ³data at the address contained in pointer ́

10x

y

Name Address Value

0x01

0x08 0x01



C and C++

C++ Improves on many of C's features

Has object-oriented capabilities

Increases software quality and reusability

Allows faster and better development of large projects Developed by B jarne Stroustrup at Bell Labs

Called "C with classes"� C++ (increment operator) - enhanced version of C

Superset of C Can use a C++ compiler to compile C programs

Gradually evolve the C programs to C++

C++ is much stricter than C

ANSI C++ Final version at http://www.ansi.org/

ANSI 1998



Some diff er ences & conventions

File extensions

C files: .c

C++ files: .cpp (which we use), .cxx, .C (uppercase)

Header files: .h

Differences

C++ allows you to "comment out" a line by preceding it with //

For example: // text to ignore

<iostream> - input/output stream header file (no .h!)

Return types - all functions must declare their return type

C does not require it, but C++ does

Variables in C++ can be declared almost anywhere

In C, required to declare variables in a block, before any

executable statements



Input/Output

Input/Output in C++ Performed with streams of characters

Streams sent to input/output objects

Data inserted into or extracted out of these streams

Output

std::cout - standard output stream (connected to screen) << stream insertion operator ("put to")

std::cout << "hi"; Puts "hi" to std::cout, which prints it on the screen

Input

std::cin - standard input object (connected to keyboard)

>> stream extraction operator ("get from")

std::cin >> myVariable; Gets stream from keyboard and puts it into myVariable



cin

Imagine a stream of data flowing from the keyboard tothe computer/memory

istream = INstream

You can extract a value from this stream

Just use the extraction operator to get a value fromthe stream of data and put it in your variable

cin >> intVariable;

intVariable



Input/Output modifiers

std::endl "end line"

Stream manipulator - prints a newline and flushes outputbuffer

Some systems do not display output until "there is enoughtext to be worthwhile" std::endl forces text to be displayed

using directive statements Allow us to remove the std:: prefix

Just add ³using namespace std;´ or ³usingstd::cout;´

Discussed further later

Cascading Can have multiple << or >> operators in a single statement

(³chaining´)std::cout << "Hello " << "there" << std::endl;

Better!



Namespaces

Sets the scope of variables and identifiers

(names), including functions!

All unnamed namespaces are in global scope Just add ³using namespace std;´ directive

Then you can just say cout instead of std::cout



IO Manipulation

Use ³#include <iomanip>´ to access the

input/output manipulation functions

setw(int) set width of the fieldsetprecision(int) sets # of decimal places

setiosflags(ios::left) set alignment, etc.



Scopes, Casts, & Manipulators

Unary scope resolution operator (::) Access global variables if a local variable has same name

Instead of variable use ::variable

static_cast <newType> (variable)

Creates a copy of variable

of typenewType

Convert ints to floats, etc.

Stream manipulators

Can change how output is formatted

setprecision - set precision for floats (default 6 digits)

setiosflags - formats output setwidth - set field width



1. Initialize globalconst PI

1.1 cast globalPI to a localfloat

2. Print local and

global values of PI

2.1 Vary precisionand print local PI

1 // casts.cpp

2 // Using the unary scope resolution operator

3 #include <iostream>

4

5 using std::cout;

6 using std::endl;

7 using std::ios;8

9 #include <iomanip>

10

11 using std::setprecision;

12 using std::setiosflags;

13 using std::setw;

14

15 const double PI = 3.14159265358979;

16

17 int main()

18 {

19 const float PI = static_cast < float >( ::PI );

20

21 cout << setprecision( 20 )

22 << " Local float value of PI = " << PI

23 << "\nGlobal double value of PI = " << ::PI << endl;

24

25 cout << setw( 28 ) << "Local float value of PI = "

26 << setiosflags( ios::fixed | ios::showpoint )

27 << setprecision( 10 ) << PI << endl;

28 return 0;

29 }Local float value of PI = 3.141592741012573242

Global double value of PI = 3.141592653589790007Local float value of PI = 3.1415927410



Typecasting

Automatic type conversion

Converted to largest data type in an expression

Right side of assignment converted to data typeof left side

Can lead to semantic errors!

02 c Cpp Differences

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