C random C ++ rand function application

Random functions are not ansi c standards and cannot be compiled by GCC, Vc, or other compilers. But in C Language int random (Num) can be used like this, it returns a random number from 0 to num-1.

You can use the rand function in C ++.

Rand () % N range 0 ~ N-1

Rand () is mainly used to generate random numbers. Others can be ignored here.

Obviously, the range of any number rand () % N is obviously 0 ~ N-1;

How to generate n ~ What about the number of M? In the same way, we only need to perform some symbolic operations on rand;

N + rand () % (m-n + 1 );

In this way, we can only analyze the seeds and floating-point numbers,

 

Next, let's talk about the usage of rand (). The floating point number is put at the end. Generally, a seed should be initialized before it is used. If you do not write it, the system will give you a default seed, below is the sample code we enter;

 

int seed;scanf ("%d",&seed);srand(seed);cout<<rand()<<endl;

 

#include <stdio.h>#include <stdlib.h>#include <time.h>int main(){    int arr[15];    //srand(time(NULL));    int seed;    while(1){    scanf("%d",&seed);    srand(seed);    for (int i=0; i<15; i++)         printf ("%d\t",rand()%10);    printf ("\n");      }    return 0;}

After comparison, it is found that every seed is a random variable value that maintains this State and will exist in the system;

Therefore, we need to keep the time difference for this initialization seed; that is to say, we still use srand (Time (null); better

The following code is suitable:

#include <stdio.h>#include <stdlib.h>#include <time.h>int main(){    //int arr[15];    srand(time(NULL)); for (int i=0; i<15; i++)         printf ("%d\t",rand()%10);    printf ("\n");      while (1);    return 0;}

Now let's talk about the last point -- random generation of floating point numbers.

Rand () % N ============= 0 ~ N-1, then we can divide it by N.

It can be expressed as: (RAND () % N)/(n * 1.0) // here note that the implicit conversion is low ------> high

The following is an example:

#include <stdio.h>#include <stdlib.h>#include <time.h>int main(){    int arr[15];    //srand(time(NULL));    int seed;    while(1){    scanf("%d",&seed);    srand(seed);    for (int i=0; i<15; i++)         printf ("%lf\t",(rand()%10)/10.0);    printf ("\n");      }    return 0;}

 

 

What if it is more accurate? What about 0.11 ??? The truth is the same.

We can output (RAND () % N)/(n * 1.0) + (RAND () % N)/(n * 10.0 );

Thus, we can sum up the rule that p represents the exact number of digits.

{P}

1 ...... 1 * (RAND () % N)/10 ^ P