Generate random ints, floats, and doubles with ease.

It is not uncommon at all for a program to require random numbers for one thing or another. For the most part the standard rand() function works just fine, but what do we do when we need to generate numbers within a range? Or what about generating random floating point numbers? Well look no further, here is a simple, but very useful, set of functions to do just that. Oh, and because I’m feeling generous I’m going to include some basic random string generation functions.

To use these functions you need to include the following files

//use this first function to seed the random number generator,
//call this before any of the other functions
void initrand()
{
    srand((unsigned)(time(0)));
}

//generates a psuedo-random integer between 0 and 32767
int randint()
{
    return rand();
}

//generates a psuedo-random integer between 0 and max
int randint(int max)
{
    return int(max*rand()/(RAND_MAX+1.0));
}

//generates a psuedo-random integer between min and max
int randint(int min, int max)
{
    if (min>max)
    {
        return max+int((min-max+1)*rand()/(RAND_MAX+1.0));
    }
    else
    {
        return min+int((max-min+1)*rand()/(RAND_MAX+1.0));
    }
}

//generates a psuedo-random float between 0.0 and 0.999...
float randfloat()
{
    return rand()/(float(RAND_MAX)+1);
}

//generates a psuedo-random float between 0.0 and max
float randfloat(float max)
{
    return randfloat()*max;
}

//generates a psuedo-random float between min and max
float randfloat(float min, float max)
{
    if (min>max)
    {
        return randfloat()*(min-max)+max;    
    }
    else
    {
        return randfloat()*(max-min)+min;
    }    
}

//generates a psuedo-random double between 0.0 and 0.999...
double randdouble()
{
    return rand()/(double(RAND_MAX)+1);
}

//generates a psuedo-random double between 0.0 and max
double randdouble(double max)
{
    return randdouble()*max;
}

//generates a psuedo-random double between min and max
double randdouble(double min, double max)
{
    if (min>max)
    {
        return randdouble()*(min-max)+max;    
    }
    else
    {
        return randdouble()*(max-min)+min;
    }
}

char* randstr(char* str, unsigned long length)
{
    //make we were passed a valid pointer
    if (!str)
    {
        return 0;
    }

    //make sure the string is supposed to contain something
    if (!length)
    {
        return 0;
    }

    //put random characters into the string, give both
    //upper and lower case numbers an equal chance at
    //being used
    for (unsigned long x=0;x<length-1;x++)
    {
        if (!randint(1))
        {
            str[x]=(char)randint(65,90);
        }
        else
        {
            str[x]=(char)randint(97,122);
        }
    }

    //null terminate the string
    str[x]=0;

    return str;
}

//flags for the extended randstr function
#define RAND_STR_CAPITOL_LETTERS    0x00000001    //65 through 90
#define RAND_STR_LOWER_CASE_LETTERS    0x00000002    //97 through 122
#define    RAND_STR_NUMBERS        0x00000004    //48 through 57
#define RAND_STR_SYMBOLS_1        0x00000008    //32 through 47
#define RAND_STR_SYMBOLS_2        0x00000010    //58 through 64
#define RAND_STR_SYMBOLS_3        0x00000020    //91 through 96
#define RAND_STR_SYMBOLS_4        0x00000040    //123 through 126
#define RAND_STR_NON_PRINTING        0x00000080    //1 through 31 and 127
#define RAND_STR_EXTENDED_ASCII        0x00000100    //128 through 255

char* randstr(char* str, unsigned long length, unsigned long flags)
{
    //make we were passed a valid pointer
    if (!str)
    {
        return 0;
    }

    //make sure the string is supposed to contain something
    if (!length)
    {
        return 0;
    }

    //if none of the flags were used then we set flags to use just upper and lower case
    if ((!flags&0x00000001)&&(!flags&0x00000002)&&(!flags&0x00000004)&&
    (!flags&0x00000008)&&(!flags&0x00000010)&&(!flags&0x00000020)&&(!flags&0x00000040)
    &&(!flags&0x00000080)&&(!flags&0x00000100))
    {
        flags=RAND_STR_LOWER_CASE_LETTERS|RAND_STR_CAPITOL_LETTERS;
    }

    char t[9]={0};
    int i=0;

    //each pass of the loop the flags are checked and for each flag that is used
    //then a random character in the flags range is added to a temporary array of
    //characters, after all the flags are checked a random character from the
    //temporary array is chosen to be inserted into the string
    for (unsigned long x=0;x<length-1;x++)
    {
        i=0;

        if (flags&0x1)
        {
            t[i]=randint(65,90);
            i++;
        }

        if (flags&0x2)
        {
            t[i]=randint(97,122);
            i++;
        }

        if (flags&0x4)
        {
            t[i]=randint(48,57);
            i++;
        }

        if (flags&0x8)
        {
            t[i]=randint(32,47);
            i++;
        }

        if (flags&0x10)
        {
            t[i]=randint(58,64);
            i++;
        }

        if (flags&0x20)
        {
            t[i]=randint(91,96);
            i++;
        }

        if (flags&0x40)
        {
            t[i]=randint(123,126);
            i++;
        }

        if (flags&0x80)
        {
            if (!randint(32))
            {
                t[i]=127;
                i++;
            }
            else
            {
                t[i]=randint(1,31);
                i++;
            }
        }

        if (flags&0x100)
        {
            t[i]=randint(127,255);
            i++;
        }

        str[x]=t[randint(i-1)];
    }

    //null terminate the string
    str[x]=0;

    return str;
}

Now you may be wondering why not just use modulous division to get random integers within a range, well the problem with doing this is that it places a greater significance on the lower order bits of the number thus making the numbers less evenly distributed (which may be what you need, but odds are you want normally distributed random numbers).