Programming with C (math library error)

[SnakeDoc]

Homework Statement

I have make a program that solves the distance between 2 points on a triangle.

Homework Equations

none

The Attempt at a Solution

/* homework 1 */

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

int main(void)
{
// Declare and initialize variables
  float x1=1, y1=5, x2=4, y2=7;
  float dx, dy, distance;

// Compute sides of a right triangle
  dx = x2 - x1;
  dy = y2 - y1;

  distance = sqrt (dx*dx + dy*dy);

// Print distance
  printf("The distance between the two points is: %5.2f \n",distance);

// Exit program
return(0);
}

I keep getting a an error about an undefined reference to sqrt
Did I do something wrong?

 

[Mark44]

Homework Statement

I have make a program that solves the distance between 2 points on a triangle.

Homework Equations

none

The Attempt at a Solution

/* homework 1 */

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

int main(void)
{
// Declare and initialize variables
float x1=1, y1=5, x2=4, y2=7;
float dx, dy, distance;

// Compute sides of a right triangle
dx = x2 - x1;
dy = y2 - y1;

distance = sqrt (dx*dx + dy*dy);

// Print distance
printf("The distance between the two points is: %5.2f \n",distance);

// Exit program
return(0);
}

I keep getting a an error about an undefined reference to sqrt
Did I do something wrong?

Your program runs fine for me, although I get this warning:

warning C4244: '=' : conversion from 'double' to 'float', possible loss of data

due to the fact that sqrt() returns a double, and you're storing the returned value in a smaller type. I suspect you don't have things set up correctly so that the compiler can't find the header files (math.h in particular).

 

[DrClaude]

Did you link to the math library (-lm flag)?

http://stackoverflow.com/questions/1033898/why-do-you-have-to-link-the-math-library-in-c

 

[HallsofIvy]

I use Pascal rather than C++ but in Pascal, if you reference a "math" library in order to use the "sqrt" function, you would have to use "math.sqrt(dx*dx+ dy*dy)".

 

[DrClaude]

I use Pascal rather than C++ but in Pascal, if you reference a "math" library in order to use the "sqrt" function, you would have to use "math.sqrt(dx*dx+ dy*dy)".

This is C, not C++, and you simply use sqrt, without a math. attached to it. You also need to #include the math header,

#include <math.h>

For historical reasons, the math functions are not part of the standard library, so the math library must be specifically linked to. For instance

gcc -O mymathcode.c -lm

 

[Mark44]

This is C, not C++, and you simply use sqrt, without a math. attached to it. You also need to #include the math header,

#include <math.h>

For historical reasons, the math functions are not part of the standard library, so the math library must be specifically linked to. For instance

gcc -O mymathcode.c -lm

I'm guessing that the OP doesn't have his compiler installation set up correctly, with the linker unable to find the code for the math library (DrClaude's earlier suggestion). Less likely, I think, is my earlier suggestion that the compiler can't find the headers, but this is still a possibility.

 

[SnakeDoc]

Did you link to the math library (-lm flag)?

http://stackoverflow.com/questions/1033898/why-do-you-have-to-link-the-math-library-in-c

Yes thank you that worked. It was actually pointed out as part of the instructions that I would need to call the math library using -lm command but I must have skip over it the first time.