当心数据类型转换发生错误

当心数据类型转换发生错误。

尽量使用显式的数据类型转换（让人 们知道发生了什么事），避免让编译器轻悄悄地进行隐式的数据类型转换。

 1 #include <iostream>
 2 #include <valarray>                 
 3 #include <math.h>                   
 4 
 5 using namespace std;
 6 
 7 #define ARRAY_SIZE  3               //array size
 8 
 9 //测试valarray容器
10 /* run this program using the console pauser or add your own getch, system("pause") or input loop */
11 
12 int main(int argc, char** argv) {
13         //创建具有3个元素的数组val_array 
14     valarray<double> val_array(ARRAY_SIZE);
15 
16     //设置数组的值为1, 4, 9
17     for (int i = 0; i < ARRAY_SIZE; i++)
18         val_array[i] = (i+1) * (i+1);
19 
20     //显示val_array数组的大小
21     cout << "Size of val_array = " << val_array.size() << endl;
22 
23     // 显示val_array数组的值
24     cout << "The values in val_array before calling sqrt() and pow():" << endl;
25     for (int i = 0; i < ARRAY_SIZE; i++)
26         cout << val_array[i] << "    ";
27     cout << endl;
28 
29     //声明一个rev_valarray数组，其保存对数组val_array的取反
30     valarray<double> rev_valarray(ARRAY_SIZE);
31     for (int i = 0; i < ARRAY_SIZE; i++)
32         rev_valarray[i] = val_array[ARRAY_SIZE - i - 1];
33 
34     //显示rev_valarray数组的大小和元素
35     cout << "Size of rev_valarray = " << rev_valarray.size() << endl;
36     cout << "The values in rev_valarray:" << endl;
37     for (int i = 0; i < ARRAY_SIZE; i++)
38         cout << rev_valarray[i] << "    ";
39     cout <<endl;
40 
41     // 声明rvalue_array数组，其存放调用sqrt()和pow()函数的返回值
42     valarray<double> rvalue_array;
43 
44     //调用sqrt()函数并显示结果
45     rvalue_array = sqrt(val_array);
46     cout << "The result of rvalue_array after calling sqrt():" << endl;
47     for (int i = 0; i < ARRAY_SIZE; i++)
48         cout << rvalue_array[i] << "     ";
49     cout <<endl;
50 
51     //对val_array数组元素计算幂函数并显示
52     rvalue_array = pow(val_array, rev_valarray);
53     cout << "The result after calling pow(val_array, rev_valarray):"
54          << endl;
55     for (int i = 0; i < ARRAY_SIZE; i++)
56         cout << rvalue_array[i] << "     ";
57     cout <<endl;
58 
59     //对val_array数组元素计算幂函数，指数均为2.0，并显示
60     rvalue_array = pow(val_array, 2.0);
61     cout << "The result after calling pow(val_array, 2.0):" << endl;
62     for (int i = 0; i < ARRAY_SIZE; i++)
63         cout << rvalue_array[i] << "     ";
64     cout <<endl;
65 
66     //对2.0进行幂函数运算，指数均为数组val_array的各元素值
67     rvalue_array = pow(2.0, val_array);
68     cout << "The result after calling pow(2.0, val_array):" << endl;
69     for (int i = 0; i < ARRAY_SIZE; i++)
70         cout << rvalue_array[i] << "     ";
71     cout <<endl;
72 
73     //对val_array和rvalue_array求和
74     cout<<"val_array.sum()="<<val_array.sum()<<endl;
75     cout<<"rvalue_array.sum()="<<rvalue_array.sum()<<endl;
76 
77     //求最大值并显示
78     cout<<"val_array.max()="<<val_array.max()<<endl;
79     cout<<"rvalue_array.max()="<<rvalue_array.max()<<endl;
80     return 0;
81 }