getchar();
putchar();
scanf();
printf();

spitze = (grenze_von + grenze_bis) / 2
x = zufallszahl(0...1) * zufallszahl(0...1)
wenn zufallszahl(0...1) < 0.5
x = x * (grenze_von - spitze)
sonst
x = x * (grenze_bis - spitze)
zufall_spitze = spitze + x

/*
Random number generator example program
This generator delivers qually distributed
real pseudo-random numbers in user-defined range
Version 1.0: range 0...1
Version 1.1: user-defined range
Version 1.2: function myrnd
It is initializes with seconds of real time
- switch off initialization to reproduce same random sequence
Version 1.2 / 2001.09.01
Autor: Peter Schindler, pstrainer@gmx.net
*/

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <conio.h>
#include <math.h>

/* ***************************************************
Declarations
*/
int myrnd_init(int myrnd_control);
float myrnd0(void);
float myrnd1(void);
float myrnd2(void);
float select_choice(void);

int user_choice;
float myrnd_max,myrnd_lo,myrnd_med,myrnd_hi;

/* ***************************************************
Main program
*/
void main (void) {

int i,j;
float r;

/* Init variables */
user_choice=9;
myrnd_lo=0.0;
myrnd_hi=0.0;

/* user info */
printf("Random number generator V1.0\n");
printf("(1) Initialize rand function with seconds(time).\n");
printf("(2) Generate & display 50 random numbers in a user-defined range.\n");
printf("(3) Display console until key pressed.\n\n");

/* Get user choice */
while (user_choice>2) {
printf("Demonstrate random function:\n");
printf(" 0-> interval 0...1\n");
printf(" 1-> user-defined interval\n");
printf(" 2-> triangle-distribution\n");
printf("Enter your choice: ");
scanf("%d",&user_choice);
if (user_choice>2) {
printf("\nError: enter 0...2 !\n\n");
}
}

/* Get limit values from user */
if ((user_choice==1)||(user_choice==2)) {
printf("\nEnter lower limit ");
scanf("%f",&myrnd_lo);
printf("Enter upper limit ");
scanf("%f",&myrnd_hi);
}

if (user_choice==2) {
myrnd_med=myrnd_hi*2.0;
while ((myrnd_med<myrnd_lo)||(myrnd_med>myrnd_hi)) {
printf("Enter peak value ");
scanf("%f",&myrnd_med);
if () {printf("Error, enter %f < peak value < %f\n",myrnd_lo,myrnd_hi);}
}
}
myrnd_init(1);

/* print 5 columns @ 10 lines of random numbers */
printf("\n");
for( i = 0; i < 10;i++ ) {
for (j=0;j<4;j++){
r = select_choice();
printf("%12f ",r);
}
r=select_choice();
printf( " %12f\n", r );
}

/* show console window until key pressed */
printf("\nType any key to continue.\n");
_getch();

}

/* ***************************************************
Function select_choice
select user choice
from avaliable functions myrnd0...myrnd2
according to int user_choice
*/
float select_choice(void)
{
float x;
x=0;
if (user_choice==0) {x=myrnd0();}
else if (user_choice==1) {x=myrnd1();}
else if (user_choice==2) {x=myrnd2();}
return(x);
}

/* ***************************************************
Function myrnd_init
int myrnd_control:
1->normalize (interval lo...hi)
2->initialize (time)
3->normalize and initialize (interval lo...hi)
*/
int myrnd_init(int myrnd_control)
{

/* normalize myrnd */
if ((myrnd_control==1)||(myrnd_control==3)) {
myrnd_max=float(RAND_MAX);
if (myrnd_max==0) {myrnd_max=1.0;}
myrnd_med=(myrnd_lo+myrnd_hi)/2.0;
}

/* initialize rand function */
if ((myrnd_control==2)||(myrnd_control==3)) {
srand (time(NULL));
}

return(myrnd_control);
}

/* ***************************************************
Function myrnd0
returns random value in interval 0...1
*/

float myrnd0(void)
{
float c;
c=float(rand())/myrnd_max;
return(c);
}

/* ***************************************************
Function myrnd1
returns random value in interval initialized by myrnd_init
*/

float myrnd1(void)
{
float c;
c=myrnd0()*(myrnd_hi-myrnd_lo)+myrnd_lo;
return(c);
}

/* ***************************************************
Function myrnd2
returns triangle-distributed random value
in interval initialized by myrnd_init
*/

float myrnd2(void)
{
float x;
x=myrnd0()*myrnd0();
if (myrnd0()<0.5) {x = x * (myrnd_lo-myrnd_med);}
else {x = x*(myrnd_hi-myrnd_med);}
x=myrnd_med+x;
return(x);
}