首先极力推荐维基百科的说明http://en.wikipedia.org/wiki/Compatibility_of_C_and_C%2B%2B
然后，一点说明
转自网络：
1--概述
Difference between c and c++
C does not have any classes or objects. It is procedure and function driven. There
is no concept of access through objects and structures are the only place where
there is a access through a compacted variable. c++ is object oriented.
C structures have a different behaviour compared to c++ structures. Structures in
c do not accept functions as their parts.
C input/output is based on library and the processes are carried out by including
functions. C++ i/o is made through console commands cin and cout.
C functions do not support overloading. Operator overloading is a process in which
the same function has two or more different behaviours based on the data input by
the user.
C does not support new or delete commands. The memory operations to free or
allocate memory in c are carried out by malloc() and free().
Undeclared functions in c++ are not allowed. The function has to have a prototype
defined before the main() before use in c++ although in c the functions can be
declared at the point of use.
After declaring structures and enumerators in c we cannot declare the variable for
the structure right after the end of the structure as in c++.
For an int main() in c++ we may not write a return statement but the return is
mandatory in c if we are using int main().
In C++ identifiers are not allowed to contain two or more consecutive underscores
in any position. C identifiers cannot start with two or more consecutive
underscores, but may contain them in other positions.
C has a top down approach whereas c++ has a bottom up approach.
Difference between c and c++ — LearnHub http://compsci.learnhub.com/lesson/page/4155-difference-between-c-and-c
1 of 2 12/28/2008 6:26 AMIn c a character constant is automatically elevated to an integer whereas in c++
this is not the case.
In c declaring the global variable several times is allowed but this is not allowed in c++.
2--实例篇
C++
Differences between C and C++
(In all the following examples, the first block of code
is C, and the next block is C++.)Memory allocation
Use new and delete instead of malloc() and
free().
-----------------------------------------------------------------
int *a;
a = (int *)malloc(20*sizeof(int));
a[19] = 10;
free(a);
-----------------------------------------------------------------
int *a;
a = new int[20];
a[19] = 10;
delete[] a;
-----------------------------------------------------------------
These operators are typed, and they also call
constructors as necessary. You should always use
new and delete with objects in C++.Pass by reference
C++ has pass-by-reference, using the & to mean the
same thing var does in Pascal.
-----------------------------------------------------------------
void swap( int *a, int *b )
{
int t;
t = *a;
*a = *b;
*b = t;
}
int x=3, y=4;
swap( &x, &y );
-----------------------------------------------------------------
void swap( int &a, int &b )
{
int t;
t = a;
a = b;
b = t;
}
int x=3, y=4;
swap( x, y );
-----------------------------------------------------------------
This means no more using crazy pointers and
address-of operators when all you want to do is pass-
by-reference.Casts
C++ has funky casts which you should become
familiar with.
-----------------------------------------------------------------
int i;
i = (int)3.14159;
-----------------------------------------------------------------
int i;
i = static_cast<int>( 3.14159 );
-----------------------------------------------------------------
You should use static_cast<>() to do any type
conversions among the basic types. There are also
dynamic, const, and reinterpret casts, which
we may run into later.Basic I/O, strings, assertions
C++ has some much nicer I/O libraries, as well as real
strings.
-----------------------------------------------------------------
#include <stdio.h>
#include <string.h>
char s[30];
printf( "Hello world, i is %d and
%d.", i++, i++ ); /*undefined*/
strcpy( s, "Bye!" );
strcat( s, s ); /* bad! */
printf( "%s\n", s );
-----------------------------------------------------------------
#include <iostream.h>
#include <assert.h>
#include <cstring.h>
cout << "Hello world, i is " <<
i++ << " and " << i++ << "." <<
endl; // well defined
string s="Bye!";
s += s; // fine
cout << s << endl;
assert( s.length() > 4 );
-----------------------------------------------------------------cout is used to output stuff to the screen. The << is
sometimes called the "put to" operator, it’s the binary
left-shift operator of C that’s been overloaded (we’ll
talk about overloading later) for stream output. It is a
nice, typesafe, unambiguous way to send output to the
screen. endl is the "end of line" string ("\n" on a
unix machine, "\r\n" on DOS, etc.).
strings work like you expect. They are actually
part of the standard class library--strings were
written in C++; they’re not "built in" to the language.
assert() is a nice macro to assert that something
is true.Booleans
C++ has booleans.
-----------------------------------------------------------------
#include <bool.h>
bool my_bool = TRUE;
if( !my_bool )
do_something();
-----------------------------------------------------------------
The only legal values of a boolean variable are TRUE
and FALSE. Of course, conditionals still accept
integers, where zero is false and non-zero is true, to
be backwards compatible with C.
Comments
C++ introduces single-line comments with //.
// This is a single-line comment.Declaration and initialization
C++ has new rules and syntax about declaration and
initialization.
-----------------------------------------------------------------
int i;
int j, k=3;
...
j = k;
for( i=0; i<N; i++ )
blah();
-----------------------------------------------------------------
int k(3);
...
int j(k);
for( int i(0); i<N; i++ )
blah();
-----------------------------------------------------------------
In C++, you should use the new style, for reasons we
will cover soon which involve constructors and
assignment operators.Constants
For those of you who do stuff like
#define MAX 20
quit it. ANSI C has const, and
const int MAX=20;
is preferred (it’s typesafe). Just a reminder. const
has other meanings in C++, which we’ll see later.Templates
C++ has templates, a way to make functions work for
many different types of arguments in a typesafe way.
-----------------------------------------------------------------
#define MAX(x,y) ((x)>(y)?(x):(y))
int x=3, y=4;
int z = MAX( x, y++ );
printf( "%d\n", y ); /* y==6 !? */
-----------------------------------------------------------------
template< class T >
T max( const T& x, const T& y )
{
if( x > y )
return x;
return y;
}
int x=3, y=4;
int z=max(x,y++);
cout << y << endl; // y==5
-----------------------------------------------------------------More templates
Here’s a C++ example of using a template to write a
generic bubble-sort on an array:
-----------------------------------------------------------------
template< class T >
void bubble_sort( T* a, int N )
// a is array, N is num elements
{
for( int i(0); i<N; i++ )
for( int j(i+1); j<N; j++ )
if( a[i] > a[j] )
swap( a[i], a[j] );
}
const int N=4;
int *ia = new int[ N ];
ia[0] = 1;
ia[1] = 4;
ia[2] = 3;
ia[3] = 2;
bubble_sort( ia, N );
for( int i(0); i<N; i++ )
cout << ia[i] << " ";
cout << endl;
-----------------------------------------------------------------
This function works on arrays of int, float,
char, string—anything with operator >
defined. Groovy.