How you calculate rand in c plus plus?

Answer 1

Use the random number generator classes.

#include<random>

#include<ctime>

std::default_random_engine generator ((unsigned)time(0)); // seed the generator

std::uniform_int_distribution<int> distribution (0, 100); // set the closed range

int r = distribution (generator); // pick a random number from 0 to 100 (inclusive)

Any device can be used to seed the generator. Here, we've simply used the current time. If you don't seed the generator, it will generate the same sequence of random values every time the program is run.

Answer 2

You don't calculate rand: you simply seed the random number generator and select a random number from the generator.

#include <iostream>

#include <time> // required for seeding

int main()

{

// Seed random number generator from current time:

srand(( unsigned ) time( NULL ));

// Set the range (1 to 10 inclusive)

int upper = 10;

int lower = 1;

// Select a random number from the range.

int r = ( rand() % (( upper - lower ) + 1 )) + lower;

return(0);

}

Answer 3

#include

And then in your code:

rand()%(n+1)

Will return an integer between 0 and n.

rand()/float(RAND_MAX)

Will return a decimal value between 0.0 and <1.0.

Answer 4

There's no way to guarantee this other than to keep track of which numbers are produced and skipping over those that have already been selected. However, keep in mind that random number generators select real numbers n such that 0.0 <= n < 1.0, and there are an infinite number of values in this range. Although many of those values cannot be represented accurately, there are still far too many to make this method practical.

Using a range of integral values is easier to check because the range of values between any two integrals is finite. Store the integrals in a vector then select an index at random (0 to n-1 for n integrals). Whichever index is chosen, swap the value at that index with the value at index n-1 (the last index). Subtract 1 from n to eliminate the last element from the next selection, repeating until n is 1. In this way every number will be selected exactly once, only the order in which they are selected will change (assuming you change the seed value on each execution). Note that the vector will contain the integrals in the reverse order they were selected. This is akin to shuffling a deck of cards by selecting a card at random and placing it in a new pile, repeating until there is only one card remaining which simply goes on top of the new pile.

Answer 5

Pseudo-random numbers can be generated with function randor random.