Linear Congruential Generator is most common and oldest algorithm for generating pseudo-randomized numbers.

The generator is defined by the recurrence relation:

Xn+1 = (aXn + c) mod c

NOTE: where

• X is the sequence of pseudo-random values.
• m, 0< m- modulus.
• a, 0< a <m- multiplier.
• c, 0< = c<m- increment.
• x0, 0⇐x0<m- the seed or start value.

The next random integer is generated using the previous random integer, the integer constants, and the integer modulus.

• To get started, the algorithm requires an initial Seed, which must be provided by some means.
• The appearance of randomness is provided by performing modulo arithmetic.

#include <iostream>
#include <cmath>
 
static const double A = 0.001342;
static const double C = 0.00025194;
static const double RAND_MAX = 1.0;
 
double rand()
{
  static double prev = 0;
  // WRONG: prev = A * prev + fmod(C, RAND_MAX);
  prev = (A * prev + C) % RAND_MAX;
  return prev;
}
 
int main(int argc, char **argv)
{
  for(int i=0; i<6; i++)
    std::cout << rand() << "\n";
  return 0;
}

returns:

0.00025194
0.000252278
0.000252279
0.000252279
0.000252279
0.000252279

This gives some nice results:

#include <iostream>
#include <cmath>
 
static const int A = 5;
static const int C = 3;
static const int RAND_MAX = 8;
 
double rand()
{
  static int prev = 1;
  // WRONG: prev = A * prev + fmod(C, RAND_MAX);
  prev = (A * prev + C) % RAND_MAX;
  return prev;
}
 
int main(int argc, char **argv)
{
  for(int i=0; i<100; i++)
    std::cout << rand() << "\n";
  return 0;
}

returns:

8
43
218
1093
5468
27343
136718
683593
3.41797e+06
1.70898e+07
8.54492e+07
4.27246e+08
2.13623e+09
2.09122e+09
1.86615e+09
7.40836e+08
-5.90786e+08
1.34104e+09
...

https://en.wikipedia.org/wiki/Linear_congruential_generator