C program to generate random numbers

This c program generates pseudo random numbers using rand and random function(Turbo C compiler only). As the random numbers are generated by an algorithm used in a function they are pseudo random, this is the reason why pseudo word is used. Function rand() returns a pseudo random number between 0 and RAND_MAX. RAND_MAX is a constant which is platform dependent and equals the maximum value returned by rand function.

C programming code using rand

We use modulus operator in our program. If you evaluate a % b where a and b are integers then result will always be less than b for any set of values of a and b. For example
For a = 1243 and b = 100
a % b = 1243 % 100 = 43
For a = 99 and b = 100
a % b = 99 % 100 = 99
For a = 1000 and b = 100
a % b = 1000 % 100 = 0

In our program we print pseudo random numbers in range [0, 100]. So we calculate rand() % 100 which will return a number in [0, 99] so we add 1 to get the desired range.

#include <stdio.h>
#include <stdlib.h>
 
int main() {
  int c, n;
 
  printf("Ten random numbers in [1,100]\n");
 
  for (c = 1; c <= 10; c++) {
    n = rand() % 100 + 1;
    printf("%d\n", n);
  }
 
  return 0;
}

If you rerun this program you will get same set of numbers. To get different numbers every time you can use: srand(unisgned int seed) function, here seed is an unsigned integer. So you will need a different value of seed every time you run the program for that you can use current time which will always be different so you will get a different set of numbers. By default seed = 1 if you do not use srand function.

C programming code using random function(Turbo C compiler only)

randomize function is used to initialize random number generator. If you don't use it then you will get same random numbers each time you run the program.

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
 
int main()
{
   int n, max, num, c;
 
   printf("Enter the number of random numbers you want\n");
   scanf("%d", &n);
 
   printf("Enter the maximum value of random number\n");
   scanf("%d", &max);
 
   printf("%d random numbers from 0 to %d are :-\n", n, max);
 
   randomize();
 
   for (c = 1; c <= n; c++)
   {
      num = random(max);
      printf("%d\n",num);         
   }
 
   getch();
   return 0;
}
randomness