[C language] random number generation and `include ＜ time. H ＞ 'learning

Catalog

One 、 Random number generation

Two 、#include The header file

3、 ... and 、 Some broken thoughts

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One 、 Random number generation

1. Pseudo random number 【rand The application of function 】

The functionality ： It can be produced randomly 0~rand_max The random number , Different definition types , The maximum value is also different .

The header file ：#include <stdlib.h>

It is called pseudo-random number , Because it is calculated according to a number and a formula , There is a high probability that the same number will be generated many times .

 #include <stdio.h>
 #include <stdlib.h>
 int main()
 {
     int a=rand();
     printf("%d",a);
     return 0;
 }

 

 

2. Random number generation 【srand Function summary 】

The function prototype ：void srand (usigned int seed);

The functionality ： Initialization function of random number generator （ Don't talk to people , It's very quiet ）

Function header file ：#include <stdlib.h> But it also needs #include <time.h> The main srand The parameters inside should be time function

 #include<stdio.h>
 #include<stdlib.h>
 #include<time.h>
 int main()
 {
     srand((unsigned)time(NULL));
     int n=rand();
     printf("%d\n",n);
     return 0;
 }

 

 

3. Generate a specific range of random numbers

(1) Produce a random number range 0~m(int type )

int a=rand()%m;

(2) Produce a random number range m~n

int a=rand()%(n-m+1)+m;

Reference blog ：http://t.csdn.cn/05x1B

Two 、#include <time.h> The header file

1. Two data types

clock_t: Measured time value （ It can only represent the time interval ）—— For program timing

time_t： Calculated distance UTC Time （1970-01-01 00:00:00） The number of seconds

Add ： A structure ---->struct tm: It can be called decomposition time , Divide time into seconds 、 branch 、 Isochronous . Usually when storing locally .

 

2. Several commonly used functions

（1）clock: Get the processor time occupied after the program starts execution , Return value clock_t.

（2）time： Get current system time （UTC Time ） Of time_t value .

（3）ctime： take time_t value transformation Is... Representing local time character string .

（4）gmttime： take time_t value transformation by Express GMT String of time .

（5）localtime： take time_t transformation by Indicates local time strunct tm structure .

（6）mktime： take Express Local time Of struct tm** Convert to time_t**.

（7）asctime： take struct tm** transformation In string form **.

（8）difftime： obtain Two calendar hours And The difference between the two .

（9）strftime： Customize the structure tm Date and time information Convert to the specified format .

Add ： The functions of this header file can be divided into two categories

（1） Time processing functions

 

（2） Time conversion function

 

3、 ... and 、 Some broken thoughts

Random numbers have been seen before , I used it a little once / two , Know it's useful , But never in-depth understanding , Just think of something you know , Guide a learning partner to ask me how to output and generate random numbers in a specific range , I just froze ……

As for this time.h The header file , I saw this random number generation again when I did the project experiment a few days ago , Sprout the library file you want to further master , To do .

But random number generation is done , But this time.h Look at the function in , Currently, there is no application scenario （ Or I can't use it ）, Plus, it's basically useless. It looks like a big nod , So it's just a simple understanding of the outline , I know there are several types , I know several functions , And I know , among time(NULL) It can be used to grow seeds .

Let's call it a day ！