Circumference of Polygon

[Prefixor]

I need some help with a program I am writing which reads type double vertices from a text file, then computes and prints the perimeter of the resultant polygon.

Every time i compile and run it, everything seems to be ok until i hit the for statement, which triggers a seg fault. Beyond that, there is probably a bigger problem, but i cannot see it.

edit: I also found another thread with a very similar topic, but even after completely duplicating the resulting program, it still gave incorrect values.

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

typedef struct {double x, y;} vertex_t;
double dist(vertex_t a, vertex_t b);

int main(void)	{
	
	FILE *fp;
	char name[64];
	double perim = 0,x,y;

	vertex_t verts[20];
	vertex_t buffer;

	int i = 0,j = 0,max = 0,status = 1;

	printf("Enter the file name: ");
	scanf("%s",name);

	fp = fopen(name,"r");
	

	while (status != EOF)	{
		status = fscanf(fp," %lf %lf ",&x, &y);
		buffer.x = x;
		buffer.y = y;
		verts[i] = buffer;
		i++;
		max++;
	}
	
	for (i = 0;i < max;j++)	{
		perim += dist(verts[j],verts[j+1]);
	}
			
	perim += dist(verts[0],verts[max]);

	printf("The perimeter is %.3lf\n",perim);

	return 0;
}

double dist(vertex_t a, vertex_t b)	{
	return sqrt(pow(b.x-a.x,2)+pow(b.y-a.y,2));
}

[nimitzhunter]

for (i = 0;i < max;j++)	{
		perim += dist(verts[j],verts[j+1]);

The problem is you increment "j" instead of "i".

[Prefixor]

ah, thats a foolish little mixup there. I fixed that whole for loop, but the program still returns incorrect values as well as reading too many lines.
For instance, when i feed in a 3 line text file, with coordinates 1 2, 2 3, and 3 4, instead of getting 4*sqrt(2) (5.657), i get 10.064.
when i insert a print statement in between the while and for loops, i is returned as 4... but it is a 3 line text file.

[Prefixor]

Nvm got it working finally. Thanks for the point out nimitz.

final working code:

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

typedef struct {double x, y;} vertex_t;
double dist(vertex_t a, vertex_t b);

int main(void)	{
	
	FILE *fp;
	char name[64];
	double perim = 0,x,y;

	vertex_t verts[20];
	vertex_t buffer;

	int i = 0,max = -1,status = 1;

	printf("Enter the file name: ");
	scanf("%s",name);

	fp = fopen(name,"r");
	

	while (status != EOF)	{
		status = fscanf(fp," %lf %lf ",&x, &y);
		buffer.x = x;
		buffer.y = y;
		verts[i] = buffer;
		i++;
		max++;
	}
	
	for (i = 0;i < (max - 1);i++)	{
			perim += dist(verts[i],verts[i+1]);
	}
			
	perim += dist(verts[0],verts[max]);

	printf("The perimeter is %.3lf\n",perim);

	return 0;
}

double dist(vertex_t a, vertex_t b)	{
	return sqrt(pow(b.x-a.x,2)+pow(b.y-a.y,2));
}