Thread: Code for random walk in 1D

hi,

Im trying to make a file with the results of the final position of 1000 1d random walks printed on it but at the moment my file seems to give the same random value 1000 times, can anyone see anyproblems with my code??

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#define N 1000


double rndm(void)
	{
		return(double)rand()/((double)RAND_MAX);
	}
	
	
/*Function to simulate random walk in 1D*/
	
double walk(int start) 
	{
	
	double a;
	int i,x;
	srand(time(NULL));
	x=start;
		
	for(i=0; i<N; i++) 
		
		{
		
		a=rndm();
		if(a<0.5) {    /*Choses which direction to move in*/
		(x=x+1);
		}
	        if (a>0.5) {
		(x=x-1);
		}   
		}
		return x; 	
		}
		
/*Main Function*/
	
int main () {
	FILE *fout;
	int i,start,random[N],x;
	srand(time(NULL));
	fout=fopen("walk.txt", "w");   //Open The File
	
	
	printf("What would you like the initial x position to be?\n:");    
	scanf("%d", &start);						//Define Start position for x 
		
	for(i=0; i<N; i++)
		{
		x=walk(start);		 // Generates Random Number
		random[i]=x;      
		fprintf(fout, "%d\n", random[i]);   // Writes Number To File
		}
	fclose(fout);                  // Closes The File
	return 0; 
		
}

Thanks!

You're calling srand everytime you call walk, you should only call srand ONCE as you do in main and keep it at that.

You're too quick, MK! That's why I edited that part out.

Originally Posted by MK27

That is definitely not the case. BTW you only need to cast the expression, not the individual numbers:

Code:

return (double)rand()/RAND_MAX;

If you only cast the expression, the division is done as an integer, and you will always get 0. Fortunately in your example, you are not casting the expression, but the result from rand(), and it is enough to cast just one of the operands.