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Zufolek on 11/24/09

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Some handy math functions

/ Published in: C

Functions for generating random numbers, flipping coins, rolling dice, etc.

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#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>

//define NDEBUG if you want to remove asserts

//the following function
//returns a random non-negative integer less than h
//h must obviously be less than or equal to the highest number
//possible from the random number generator

int rnd(int h){
 if(!h)return 0;//making sure we don't divide by zero!
 assert(h<=RAND_MAX);
 return rand()%h;
}

//rolls a virtual die
//(die is the singular of dice)
//returns a number 1-6

int rolldie(){
 return rnd(6)+1;
}

//flips a virtual coin
//returns 1 or 0 for heads or tails

int flipcoin(){
 return rand()&1;
}

//returns a floating point number in range 0 to 1

double frand(){
 return rand()/((double)RAND_MAX+1);
}

//returns random floating point number in range 0 to f

double frnd(float f){
 return frand()*f;
}

//returns 1 (true) at probability p
//example:
//prob(0.7) will be true 70% of the time

int prob(float p){
 if(frand()<p)return 1;
 return 0;
}

//returns distance between two points in 2 dimensions

double dist2d(float x1,float y1,float x2,float y2){
 float dx=x1-x2;
 float dy=y1-y2;
 return sqrt(dx*dx+dy*dy);
}

//returns distance between two points in 3 dimensions

double dist3d(float x1,float y1,float z1,float x2,float y2,float z2){
 float dx=x1-x2;
 float dy=y1-y2;
 float dz=z1-z2;
 return sqrt(dx*dx+dy*dy+dz*dz);
}

//Like % (modulus) but works "correctly" for negative values

signed int zmod(signed int a,unsigned int b){
 signed int c=0;
 if(!b)return c;//making sure we don't divide by zero
 if(a<0)--a;
 c=a%b;
 return c;
}

//returns volume of sphere having radius r
//the parentheses may help compiler optimize

double spherevolume(float r){
 return (M_PI*4/3)*(r*r*r);
}

//returns surface area of sphere having radius r

double spheresurface(float r){
 return (M_PI*4)*(r*r);
}

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