Random number
There are several ways to generate numbers in a specified range, some better than others. One method:
random_integer = (rand()%10);
This will generate numbers in the range 0 to 9. To use a non-zero baseline you can do the following:
random_integer = 20 + (rand()%10);
This will generate numbers in the range 20 to 29.
The above method of producing pseudo random numbers is poor because it only uses the low-order bits of the number returned from rand() and these may be less random for some pseudo random number generator implementations.
For a better method you should prefer the following:
random_integer = 20 + int(10.0 * rand()/(RAND_MAX+1.0));
random_integer = (rand()%10);
This will generate numbers in the range 0 to 9. To use a non-zero baseline you can do the following:
random_integer = 20 + (rand()%10);
This will generate numbers in the range 20 to 29.
The above method of producing pseudo random numbers is poor because it only uses the low-order bits of the number returned from rand() and these may be less random for some pseudo random number generator implementations.
For a better method you should prefer the following:
random_integer = 20 + int(10.0 * rand()/(RAND_MAX+1.0));
Here's how you would do it:
EDIT: Balls, got beaten again! Anyway, his way's better. Mine's just simpler but not as powerful.
#include <iostream>#include <cstdlib>#include <ctime> // Allows for better randomisation based on the current system timesrand(time(0)); // Seeds the randomiser before it can be used - time ensures that it's different everytime the program runsint RandomNumber=rand()%9+1; // 1 is the lowest it can be - 9 is the highestEDIT: Balls, got beaten again! Anyway, his way's better. Mine's just simpler but not as powerful.
ciao,
try the most simple way:
int nNumber = rand() % 9;disclaimer: this is the most simple way; and you shouldn't expect too much from this construction.
#include <iostream> // For cout and endl#include <cstdlib> // For srand and rand#include <ctime> // For timeusing namespace std; // Make the code easyer to read.int main(){ srand(time(0)); // Do this ONCE. int x = rand()%9+1; // This isnt very good but it works. cout << x << endl; // Show the number. return 0;}
don't forget,.....
#include <cstdlib>
or maybe it was
#include <math.h> hmmmmmm you guys would know..
#include <cstdlib>
or maybe it was
#include <math.h> hmmmmmm you guys would know..
Here is what you need to know.
RAND_MAX is a constant that gives the highest number generated by rand();
rand(): a function that returns an integer between 0 and RAND_MAX
srand(int): "Seeds" the rand function. An integer is used as a seed.
Typically, this integer is generated by using some kind of time function.
Dissecting it :
(float)rand()/ RAND_MAX gives a number between 0 and 1, since RAND_MAX is the highest possible value.
We then add the lower bound to that number, and multiply it by the difference between the upper and lower bound to get a number i a given range.
RAND_MAX is a constant that gives the highest number generated by rand();
rand(): a function that returns an integer between 0 and RAND_MAX
srand(int): "Seeds" the rand function. An integer is used as a seed.
Typically, this integer is generated by using some kind of time function.
#include <cstdlib>#include <ctime>#include <iostream>int main(){ int upperBound = 9; int lowerBound = 1; //Initial seed (typically only once in a program) srand((unsigned)time( NULL ) ); //prints 5 floating point number between lowerBound and upperBound. for (int i = 0; i < 5; i++) { cout << (((float)rand()/ RAND_MAX) + lowerBound) * (upperBound-lowerBound); } return 0;} Dissecting it :
(float)rand()/ RAND_MAX gives a number between 0 and 1, since RAND_MAX is the highest possible value.
We then add the lower bound to that number, and multiply it by the difference between the upper and lower bound to get a number i a given range.
Here's a link to a C++ Random Number Tutorial that explains how to do it in a clearer fashion than I could.
Author
The number seems to be the the same everytime i restart my program. I've used everything you've posted
Quote:Original post by Yhack
The number seems to be the the same everytime i restart my program. I've used everything you've posted
You need to do the srand() call.
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