Problems with Sqrt()

nostrum · 07-16-2004, 10:23 AM

Hi I'm basically having trouble getting this program to compute the distance between two points and according to gcc with -Wall flag enabled it's because sqrt() is an "undefined reference to sqrt", another thing people might want to notice is I used y3 instead of y1 because apparently according to gcc y1 is already taken variable. Any ideas why that is? Basically I just need to figure out the right syntax for sqrt() so any help would be greatly appreciated. Now here's the code:

/* Distance.C - Calculates the distance between two points on a plane */
#include <stdio.h>
#include <math.h>

char line[100]; /* line of input data */
double x1; /* coordinance of the first x coordinance */
double x2; /* coordinance of the seocnd x coordinance */
double y3; /* coordinance of the first y coordinance */
double y2; /* coordinance of the second y coordinance */
double distance; /* the distance between the two points */
double x; /* the square of the first coordinance */
double y; /* the square of the second coordinance */

int main()
{
printf("What are the coordinances of the two points(Use the format x1 y1 x2 y2)? ");

fgets(line, sizeof(line), stdin);
sscanf(line, "%lf %lf %lf %lf", &x1, &y3, &x2,&y2);

x = x2 - x1;
y = y2 - y3;
/* partial = ((x * x) + (y * y)); This was an attempt to get around the problem by using
a variable named partial and then just doing distance = sqrt(partial), but that dind't
workl either */

distance = sqrt((x * x) + (y * y));
printf("The distance between the points is %lf\n", distance);
return (0);
}

backer · 07-16-2004, 11:37 AM

when you use something from math.h you have to link with libmath, using -lm on
the command line.

SETXBera · 04-15-2005, 12:24 PM

nostrum, are you going through the Practical C Programming book by O'Reilly? If so, I am too and did my a little different.

For the variables i made them float instead of double to save memory, and my math was done a little different.

I did:

Code:

/*This program will find the distance between two points on a grid*/
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

char line[10];/*input data to be converted*/
float xcoordf;/*first X coordinate*/
float ycoordf;/*first Y coordinate*/
float xcoords;/*second X coordinate*/
float ycoords;/*second Y coordinate*/
float xanswer;/*difference in X coordinates*/
float yanswer;/*difference in Y coordinates*/
float answer;/*average of the difference in both coordinates*/

main()
{
  (void)printf("Distance between two points.\n
      Enter the first x,y coordinates(using this format, no commas: x1 y1):");
  (void)fgets(line,sizeof(line),stdin);
  (void)sscanf(line,"%f %f",&xcoordf,&ycoordf);
 
  (void)printf("Enter the second set of coordinates(x2 y2, no commas):");
  (void)fgets(line,sizeof(line),stdin);
  (void)sscanf(line,"%f %f",&xcoords,&ycoords);
  
  xanswer=(xcoords-xcoordf)*(xcoords-xcoordf);
  yanswer=(ycoords-ycoordf)*(ycoords-ycoordf);
  answer=sqrt(xanswer+yanswer);
  (void)printf("The difference in the two points is %.2f.\n",answer);
  return(0);
}

Was running into the same brickwall as you until I linked to libmath under the suggestion of backer. Compiles and links with no errors or warnings of any kind.

Before I picked up Practical C Programming I was using C For Dummies, that book really walked you along slowly. I do not recommend it for anyone with a working knowledge of computers.