Rand () and srand () [C language library function source code]

[C language library function source code]

[This program is compiled in Dev C ++ 4.9.9.2]

/*

These two functions are programs that generate random numbers in the C library. You need to first

Use the srand () function to assign a random seed value. And then use

Rand () function to generate a random number. But the algorithm that generates random numbers

Relatively simple, the srandom () and random () functions are for these two functions

And the usage is similar.

*/

# Define random_max 0x7fffffff

 

Static long my_do_rand (unsigned long * value)

{

/*

This algorithm ensures that the generated value does not exceed (2 ^ 31-1)

Here (2 ^ 31-1) is 0x7fffffff. 0x7fffffff

Equal to 127773*(7 ^ 5) + 2836,7 ^ 5 = 16807.

The entire algorithm is through: t = (7 ^ 5 * t) mod (2 ^ 31-1)

This formula is used to calculate the random value and take the obtained value

The Random Seed value calculated next time.

*/

Long quotient, remainder, T;

 

Quotient = * value/127773l;

Remainder = * value % 127773l;

T = 16807l * remainder-2836l * quotient;

 

If (T <= 0)

T + = 0x7fffffffl;

Return (* value = T) % (unsigned long) random_max + 1 ));

}

Static unsigned long next = 1;

Int my_rand (void)

{

Return my_do_rand (& next );

}

 

Void my_srand (unsigned int seed)

{

Next = seed;

}

 

# Include <time. h>

Int main ()

{

Int I;

My_srand (unsigned) (Time (null )));

For (I = 0; I <100; I ++)

{

If (I % 10 = 0)

Printf ("/N ");

Printf ("% d/T", my_rand () % 99 + 1 );

}

System ("pause ");

Return 0;

}