Question: > 
> **Possible Duplicates:**  
> 
> [How to generate a random number in C?](https://stackoverflow.com/questions/822323/how-to-generate-a-random-number-in-c)  
> 
> [implementation of rand()](https://stackoverflow.com/questions/1167253/implementation-of-rand)  
> 
> [Generating random terrain in Blender3D](https://stackoverflow.com/questions/31834/generating-random-terrain-in-blender3d) 
> 
> 
> 

I need high quality random numbers in C, but I have no idea what to really do. I need to be able to get numbers from 1-100. Any help or maybe point me to where I can find help.

Answer: 
This is the simplest method of producing uniformly distributed random numbers in C:

**Step 1.** Be sure to include the standard library header to get the necessary function prototypes

```
#include <stdlib.h>

```

**Step 2.** Seed the random number generator using `srand()`. The seed determines where the random numbers start. The sequence of random numbers will always be exactly the same for a given seed. This allows you to have random, yet reproducible results. If you don't need it to be reproducible, a good thing to seed with is the current time, so that the random sequence will be different on each run.

```
srand(time(NULL));

```

(be sure to include time.h if you do this). Also, *only seed the generator once per program run* unless you are generating a huge number (millions or billions) of random numbers. Seeding frequently makes the sequence *less* random.

**Step 3.** Get your random number.

```
rand()

```

This function returns a random number between 0 and RAND\_MAX, which is a macro that is defined as a rather large integer.

**Step 4.** Get your random number into the range you want. The general formula for doing so is this:

```
int random_number = rand() % range + min;

```

Where range is how many (consecutive) numbers you want to choose from, and min is the smallest of these. So to generate a number between 1 and 100, range is 100 and min is 1:

```
int random_number = rand() % 100 + 1;

```

Some people object to this formula because it uses the low-order bits of the number given by rand(), and in older implementations of software pseudo-random number generators these were often less random than the high order bits, but on any modern system this method should be perfectly fine.
The other posts have good advice. If you really want to dive into the guts of random number generation, take a look at [Numerical Recipes in C](http://www.nrbook.com/a/bookcpdf.php). Start with [Chapter 7](http://www.nrbook.com/a/bookcpdf/c7-0.pdf).