## How to generate different random numbers in a loop in C++?

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Is it possible to generate different random number, every time loop runs. For example, i have:

for (int t=0;t<10;t++) { int random_x; srand ( time(NULL) ); random_x = rand() % 100; cout<<"\nRandom X = "<<random_x; }

But the problem is, it generates same random number everytime. Is it possible to generate different random numbers everytime loop runs?

IS there any possibility to reset random number initiallization as well?

Don't use `srand`

inside the loop, use it only once, e.g. at the start of `main()`

. And `srand()`

is exactly how you reset this.

**How to generate different random numbers in a loop in C++?,** The function void srand(unsigned int seed) seeds the random number generator used by the function rand. The declaration of srand() is like I'm trying to make a dice game that uses 6 dice. I can generate a random number each roll, the problem is that I keep getting that same number (if the generated number is 1, each dice is 1).

You are getting the same random number each time, because you are setting a seed inside the loop. Even though you're using `time()`

, it only changes once per second, so if your loop completes in a second (which it likely will), you'll get the same seed value each time, and the same initial random number.

Move the `srand()`

call outside the loop (and call it only once, at the start of your app) and you should get random "random" numbers.

**How do I generate different random numbers in a loop in C?,** Just put this in the for loop: r = (rand()%6)+1;. And declare r outside of it like this: int r;. OR you don't use r and the program would look One mathematical function in C programming that’s relatively easy to grasp is the rand () function. It generates random numbers. Though that may seem silly, it’s the basis for just about every computer game ever invented. Random numbers are a big deal in programming. A computer cannot generate truly random numbers.

Do **not** use `rand()`

; use new C++11 facilities (e.g. ** std::mt19937**,

**, etc.) instead.**

`std::uniform_int_distribution`

You can use code like this (**live here on Ideone**):

#include <iostream> #include <random> using namespace std; int main() { // Random seed random_device rd; // Initialize Mersenne Twister pseudo-random number generator mt19937 gen(rd()); // Generate pseudo-random numbers // uniformly distributed in range (1, 100) uniform_int_distribution<> dis(1, 100); // Generate ten pseudo-random numbers for (int i = 0; i < 10; i++) { int randomX = dis(gen); cout << "\nRandom X = " << randomX; } }

**P.S.**

Consider watching this video from Going Native 2013 conference for more details about `rand()`

-related problems:

**How to generate different random numbers in a loop in C++?,** Don't use srand inside the loop, use it only once, e.g. at the start of main() . And srand() is exactly how you reset this. Depends on what you want to do with the random numbers… The header file stdlib.h has the function rand(), which gives you (pseudo-)random integers from 0 to RAND_MAX (a very high number defined in the file—for GNU, it’s 2147483647).

Try moving the seed `srand`

outside the loop like so:

srand ( time(NULL) ); for (int t=0;t<10;t++) { int random_x; random_x = rand() % 100; cout<< "\nRandom X = "<<random_x; }

As Mark Ransom says in the comment, moving the seed outside the loop will only help if the loop is not residing in a function you are calling several times.

**Unique Random Numbers,** The goal is to write code that generates random numbers, but never the loop until a valid card is drawn */ { c = rand() % CARDS; /* generate C program to generate 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 that word pseudo is used. Function rand() returns a pseudo-random number between 0 and RAND_MAX.

I had this same problem for days. Keeping srand() out of the loop is a +. Also, dont assign rand() % 100 to any variable. Simply cout rand() % 100 in the loop. Try this:

srand (time(NULL)); (int t=0;t<10;t++) { cout << rand() % 100 << endl; }

**How can I generate different random Numbers from Code in C Prog?,** I am trying to take multiple runs and to get different output files using batch file. The source file includes random number generator. But it always gives same rand () rand () function is used in C to generate random numbers. If we generate a sequence of random number with rand () function, it will create the same sequence again and again every time program runs.

**rand() and srand() in C/C++,** rand() function is used in C to generate random numbers. Say if we are generating 5 random numbers in C with the help of rand() in a loop, then every time we compile Any other value for seed sets the generator to a different starting point. Output contains 5 random numbers in given range. As C does not have an inbuilt function for generating a number in the range, but it does have rand function which generate a random number from 0 to RAND_MAX. With the help of rand a number in range can be generated as num = (rand() % (upper – lower + 1)) + lower

**C program to generate random numbers,** C program to generate pseudo-random numbers using rand and random function To get different numbers every time you can use: srand(unsigned int seed) You are getting the same random number each time, because you are setting a seed inside the loop. Even though you're using time(), it only changes once per second, so if your loop completes in a second (which it likely will), you'll get the same seed value each time, and the same initial random number.

**How to Generate Random Numbers in C Programming,** The rand() function is the simplest of C's random-number functions. It requires the Now, That's Random uses a nested for loop to display 100 random values. The rand() Run the program a few times, trying different seed values. The output

##### Comments

- Reading the documentation for
`srand()`

might be useful. - Just to make Noah's comment at bit more helpful: cplusplus.com/reference/clibrary/cstdlib/srand :)
- possible duplicate of Always repeated numbers given by rand()
- +1 for "same random number every time" (lol!)
- Removed the
`[c]`

tag, since the question has "**C++**" in the title. - I did this, but it changes random value only once now. As forexample it generates 15, 23, 23, 23, 23. Now what shall I do?
- If you really put it at the start of main(), you wouldn't be getting that sequence.
- Still if u execute program more than once with in second, random number sequence will be the same
- Moving it outside the loop might not be enough, as the loop might be called more than once a second.
- I did this, but it changes random value only once now. As forexample it generates 15, 23, 23, 23, 23. Now what shall I do?
- Also note that
`srand()`

is very expensive compared to`rand()`

. In glibc this is guaranteed by the fact that in addition to the initial setup done by`srand()`

it calls`rand()`

300+ times to stir the pot. - As a sanity check, take off the
`% 100`

and look at the raw values returned by`rand`

. Using the`%`

operator to map into a range of values may result in a non-normal distribution depending on the RNG being used, as the low-order bits may*not*be entirely random. A better method is to do something like`val = min + (int) ((double) rand() / RAND_MAX * (max - min + 1);`

to map into the range [min,max]. - Moving it outside the loop might not be enough, as the loop might be called more than once a second.
- I did this, but it changes random value only once now. As forexample it generates 15, 23, 23, 23, 23. Now what shall I do?