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C++ Note 1

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可读性差,只留着自己用
[cpp]
// my first program in C++

/* my second program in C++
with more comments */

#include
using namespace std;

int main ()
{ cout << "Hello World!";
return 0;
} [/cpp]

Name Description Size* Range*
char Character or small integer. 1byte signed: -128 to 127
unsigned: 0 to 255
short int (short) Short Integer. 2bytes signed: -32768 to 32767
unsigned: 0 to 65535
int Integer. 4bytes signed: -2147483648 to 2147483647
unsigned: 0 to 4294967295
long int (long) Long integer. 4bytes signed: -2147483648 to 2147483647
unsigned: 0 to 4294967295
bool Boolean value. It can take one of two values: true or false. 1byte true or false
float Floating point number. 4bytes +/- 3.4e +/- 38 (~7 digits)
double Double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)
long double Long double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)
wchar_t Wide character. or 4 bytes 1 wide character

\n newline
\r carriage return
\t tab
\v vertical tab
\b backspace
\f form feed (page feed)
\a alert (beep)
\' single quote ()
\" double quote ()
\? question mark (?)
\\ backslash (\)

[cpp]
// In order to use a variable in C++
// we must first declare it specifying which data type we want it to be.
int a, b, c;

// Signed types can represent both positive and negative values
// whereas unsigned types can only represent positive values (and zero).
unsigned short int NumberOfSisters;
signed int MyAccountBalance;

int a = 0;
int a (0);

string mystring = "This is a string";
string mystring ("This is a string");

// String literals can extend to more than a single line of code by
// putting a backslash sign (\) at the end of each unfinished line.
"string expressed in \
two lines"

//does not require a semicolon (;)
#define PI 3.14159
#define NEWLINE ‘\n’

const int pathwidth = 100;
const char tabulator = ‘\t’;

// +, -, *, /, %
// +=, -=, *=, /=, %=, >>=, <<=, &=, ^=, |=
// ++, –
// ==, !=, >, <, >=, <=

7==5 ? 4 : 3 // returns 3, since 7 is not equal to 5.
7==5+2 ? 4 : 3 // returns 4, since 7 is equal to 5+2.
5>3 ? a : b // returns the value of a, since 5 is greater than 3.
a>b ? a : b // returns whichever is greater, a or b.

a = (b=3, b+2);
// Would first assign the value 3 to b, and then assign b+2 to variable a.
// variable a would contain the value 5 while variable b would contain value 3.

// Bitwise Operators ( &, |, ^, ~, <<, >> )

int i;
float f = 3.14;
i = (int) f;
i = int ( f );

// returns the size in bytes of that type or object:
a = sizeof (char);

cout << "Hello, I am " << age << " years old and my zipcode is " << zipcode;
// Hello, I am 24 years old and my zipcode is 90064
cout << "First sentence.\n";
cout << "First sentence." << endl;

// Standard Input (cin).
int age;
cin >> age;

// to request more than one datum input from the user:
cin >> a >> b;

// In order to get entire lines, we can use the function getline,
// which is the more recommendable way to get user input with cin
#include <iostream>
#include <string>
using namespace std;

int main ()
{ string mystr;
cout << "What’s your name? ";
getline (cin, mystr);
cout << "Hello " << mystr << ".\n";
cout << "What is your favorite team? ";
getline (cin, mystr);
cout << "I like " << mystr << " too!\n";
return 0;
}

// The standard header file <sstream> defines a class called stringstrea
// that allows a string-based object to be treated as a stream.
// This way we can perform extraction or insertion operations from/to strings,
// which is especially useful to convert strings to numerical values and vice versa.
// For example, if we want to extract an integer from a string we can write:
string mystr ("1204");
int myint;
stringstream(mystr) >> myint;

// stringstreams
#include <iostream>
#include <string>
#include <sstream>
using namespace std;

int main ()
{ string mystr;
float price=0;
int quantity=0;

cout << "Enter price: ";
getline (cin,mystr);
stringstream(mystr) >> price;
cout << "Enter quantity: ";
getline (cin,mystr);
stringstream(mystr) >> quantity;
cout << "Total price: " << price*quantity << endl;
return 0;
}

if (x == 100)
cout << "x is 100";

if (x == 100)
{ cout << "x is ";
cout << x;
}

if (x == 100)
cout << "x is 100";
else
cout << "x is not 100";

if (x > 0)
cout << "x is positive";
else if (x < 0)
cout << "x is negative";
else
cout << "x is 0";

while (n>0) {
cout << n << ", ";
–n;
}

do {
cout << "Enter number (0 to end): ";
cin >> n;
cout << "You entered: " << n << "\n";
} while (n != 0);

for (int n=10; n>0; n–) {
cout << n << ", ";
}

for ( n=0, i=100 ; n!=i ; n++, i– )
{ // whatever here…
}

for (n=10; n>0; n–)
{
cout << n << ", ";
if (n==3)
{
cout << "countdown aborted!";
break;
}
}

for (int n=10; n>0; n–) {
if (n==5) continue;
cout << n << ", ";
}

int n=10;
loop:
cout << n << ", ";
n–;
if (n>0) goto loop;

// exit is a function defined in the cstdlib library.
// to terminate the current program with a specific exit code.
void exit (int exitcode);

// Functions
int addition (int a, int b)
{ int r;
r=a+b;
return (r);
} int main ()
{ int z;
z = addition (5,3);
cout << "The result is " << z;
return 0;
}

// void function example
void printmessage ()
{ cout << "I’m a function!";
} int main ()
{ printmessage ();
// printmessage; wrong!!!
return 0;
}

[/cpp]

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