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# C ++ digital

Usually, when we need to use numbers, we use the original data types, such as int, short, long, float, and double, and so on. These data types for numbers, its possible values ​​and range of values, we have already discussed in C ++ data type chapter.

## C ++ custom number

We have chapters in various instances before the defined number. Here is a C ++ define the various types of digital integrated example:

```#include <iostream>
using namespace std;

int main ()
{
// 数字定义
short  s;
int    i;
long   l;
float  f;
double d;

// 数字赋值
s = 10;
i = 1000;
l = 1000000;
f = 230.47;
d = 30949.374;

// 数字输出
cout << "short  s :" << s << endl;
cout << "int    i :" << i << endl;
cout << "long   l :" << l << endl;
cout << "float  f :" << f << endl;
cout << "double d :" << d << endl;

return 0;
}
```

When the above code is compiled and executed, it produces the following results:

```short  s :10
int    i :1000
long   l :1000000
float  f :230.47
double d :30949.4
```

## C ++ math

In C ++, you can create a variety of functions in addition, also contains a variety of useful functions for you to use. These functions are written in standard C and C ++ libraries, calledbuilt-in functions.You can refer to these functions in the program.

C ++ built a wealth of mathematical functions can be performed on a variety of digital computing. The following table lists the C ++ some useful built-in mathematical functions.

To use these functions, you need to refer to mathematic header<cmath>.

1double cos(double);

2double sin(double);

3double tan(double);

4double log(double);

5double pow(double, double);

6double hypot(double, double);

7double sqrt(double);

8int abs(int);

9double fabs(double);

10double floor(double);

Here is a simple example of mathematical operations:

```#include <iostream>
#include <cmath>
using namespace std;

int main ()
{
// 数字定义
short  s = 10;
int    i = -1000;
long   l = 100000;
float  f = 230.47;
double d = 200.374;

// 数学运算
cout << "sin(d) :" << sin(d) << endl;
cout << "abs(i)  :" << abs(i) << endl;
cout << "floor(d) :" << floor(d) << endl;
cout << "sqrt(f) :" << sqrt(f) << endl;
cout << "pow( d, 2) :" << pow(d, 2) << endl;

return 0;
}
```

When the above code is compiled and executed, it produces the following results:

```sign(d) :-0.634939
abs(i)  :1000
floor(d) :200
sqrt(f) :15.1812
pow( d, 2 ) :40149.7
```

## C ++ Random Number

In many cases, we need to generate a random number. Random number generator, there are two related functions. One is therand (), the function only returns a pseudo-random number.You must callsrand () function before generating a random number.

Here is a simple example of generating random numbers. Examples of the use oftime () function to obtain the number of seconds the system time, function to generate a random number by calling the rand ():

```#include <iostream>
#include <ctime>
#include <cstdlib>

using namespace std;

int main ()
{
int i,j;

// 设置种子
srand( (unsigned)time( NULL ) );

/* 生成 10 个随机数 */
for( i = 0; i < 10; i++ )
{
// 生成实际的随机数
j= rand();
cout <<"随机数： " << j << endl;
}

return 0;
}
```

When the above code is compiled and executed, it produces the following results:

```随机数： 1748144778

```