hey guys thanks for reading this.. i know that its a simple error on my part as i dont really know what im doing..

Am using this "Numerical recipes in C" to help me with some complex maths, but my programming skills are shot. The book can be found in web-form at http://www.ma.utexas.edu/documentation/nr/bookcpdf.html if required, im using the ran2 function.

The function should run fine, as its straight from the books data cd, but im not sure how i get it running.

It always returns the same (large) number. It says i initialize with a negative integer call to "idum" but im not sure how to do this.

Hope its all commented easy and i do the code tages right!

Any help much appreciated!!!Code:/* random number between 0 and 1 using ran2 method p282*/ #include <stdio.h> #include <stdlib.h> #define IM1 2147483563 #define IM2 2147483399 #define AM (1.0/IM1) #define IMM1 (IM1-1) #define IA1 40014 #define IA2 40692 #define IQ1 53668 #define IQ2 52774 #define IR1 12211 #define IR2 3791 #define NTAB 32 #define NDIV (1+IMM1/NTAB) #define EPS 1.2e-7 #define RNMX (1.0-EPS) /*Long period (>2e10^18) random number generator of L'Ecuyer with Bays-Durham shuffle and added safeguards. Returns a random deviate between 0.0 and 1.0 (exlclusive of the endpoint values). Call with idum a negative integer to initialize; thereafter do not alter idum between successive deviates in a sequence. RNMX should approxiamte the largest floating value that is less than 1. */ float ran2(long *idum); /*this bit i entered i doubt it is even close to being correct i always get the same number, which isnt even in the range 0.0 to 1.0!*/ int main() { float answer; long *pointer; long initial = -0.2; /*it says im supposed to initialise with a call to idum, am i doing that here?*/ pointer=&initial; answer=ran2(pointer); printf ("%d", answer); printf ("\nPress ENTER to continue.\n"); fflush (stdin); (void) getchar(); return (0); } /*end of bit i entered!*/ /*this is the ran2 function listed in the book, straight from the cd*/ float ran2(long *idum) { int j; long k; static long idum2=123456789; static long iy=0; static long iv[NTAB]; float temp; if (*idum <= 0) { if (-(*idum) < 1) *idum=1; else *idum = -(*idum); idum2=(*idum); for (j=NTAB+7;j>=0;j--) { k=(*idum)/IQ1; *idum=IA1*(*idum-k*IQ1)-k*IR1; if (*idum < 0) *idum += IM1; if (j < NTAB) iv[j] = *idum; } iy=iv[0]; } k=(*idum)/IQ1; *idum=IA1*(*idum-k*IQ1)-k*IR1; if (*idum < 0) *idum += IM1; k=idum2/IQ2; idum2=IA2*(idum2-k*IQ2)-k*IR2; if (idum2 < 0) idum2 += IM2; j=iy/NDIV; iy=iv[j]-idum2; iv[j] = *idum; if (iy < 1) iy += IMM1; if ((temp=AM*iy) > RNMX) return RNMX; else return temp; } #undef IM1 #undef IM2 #undef AM #undef IMM1 #undef IA1 #undef IA2 #undef IQ1 #undef IQ2 #undef IR1 #undef IR2 #undef NTAB #undef NDIV #undef EPS #undef RNMX /* (C) Copr. 1986-92 Numerical Recipes Software ]y. */