1 #include <stdio.h>
 2 
 3 const char endl = ‘\n‘;
 4 
 5 class Console
 6 {
 7 public:
 8     Console& operator << (int i)
 9     {
10           printf("%d", i);
11           return *this;
12     }
13     
14         Console& operator << (char c)
15     {
16           printf("%c", c);
17           return *this;
18     }
19     
20     Console& operator << (const char* s)
21     {
22           printf("%s", s);
23           return *this;          
24     }
25     
26         Console& operator << (double d)
27     {
28           printf("%f", d);
29           return *this;          
30     }
31 };
32 
33 Console cout;
34 
35 int main()
36 {
37     cout << 1 << endl;               //1
38     cout << "Hello World!" << endl;  //Hello World!
39     
40     double a = 0.1;
41     double b = 0.2;
42     
43     cout << a + b << endl;          //0.300000
44 
45     return 0;
46 }

 1 /*
 2 //C++编译商提供的C兼容库（既不是C++标准库提供的,也不是C语言库文件，而是一种兼容库）
 3 #include <stdio.h>
 4 #include <string.h>
 5 #include <stdlib.h>
 6 #include <math.h>
 7 */
 8 
 9 //C++标准库提供的C兼容库
10 #include <cstdio>
11 #include <cstring>
12 #include <cstdlib>
13 #include <cmath>
14 
15 using namespace std; //位于std命名空间中
16 
17 int main()
18 {
19     //以下的代码是使用C++标准库提供的C兼容库写的，
20     //从形式上看，与C代码写的完全一样，这就是C++
21     //为C提供了很好的支持的例子！
22     printf("hello world!\n");
23     
24     char* p = (char*)malloc(16);
25     
26     strcpy(p, "");
27     
28     double a = 3;
29     double b = 4;
30     double c = sqrt(a * a + b * b);
31     
32     printf("c = %f\n", c);
33     
34     free(p);
35 
36     return 0;
37 }

 1 #include <iostream> //使用C++标准库的输入输出
 2 #include <cmath>
 3 
 4 using namespace std; //位于std命名空间中
 5 
 6 int main()
 7 {
 8     cout << "Hello world!" << endl;
 9     
10     double a = 0;
11     double b = 0;
12     
13     cout <<"Input a:";
14     cin >> a;
15     
16     cout <<"Input b:";
17     cin >> b;
18     
19     double c = sqrt(a * a + b * b);
20     
21     cout << "c = "<< c << endl;
22 
23     return 0;
24 }