I just change to sprintf(result,"%.2f%.2f",polygon_area, perim); The actual code is now this:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
enum { x, y};
typedef struct triangle{
double v1[2];
double v2[2];
double v3[2];
} triangle;
double area(triangle a);
double perimeter(double* vertices, int size);
double side(double* p1, double* p2);
char expected[] = "80.0036.00";
char expected1[] = "48.0032.00";
char expected2[] = "61.5034.87";
char result[] = "";
int main()
{
int n, idx;
int triangles;
int index;
int xycount;
double xy;
double triangle_area;
double polygon_area;
double perim;
double polygon_vertices[50] = {0.0};
triangle a;
FILE* data;
char line[256];
char* token;
if ((data = fopen("C:\\Users\\CHK\\Desktop\\coordinates.txt", "r")) == NULL) {
fprintf(stderr, "can't open data file\n");
exit (EXIT_FAILURE);
}
while (fgets(line, sizeof (line), data)){
xycount = 0;
polygon_area = 0;
a = *(triangle*)malloc(sizeof (triangle));
memset(polygon_vertices, 0, sizeof (polygon_vertices));
line[strlen(line) - 1] = 0;
token = strtok(line, " ");
while (token != NULL){
xy = atof(token);
token = strtok(NULL, " ");
polygon_vertices[xycount++] = xy;
}
idx = 0;
triangles = (xycount / 2) - 2;
for (index = 2, idx = 0;idx < triangles;index += 2, ++idx){
a.v1[x] = polygon_vertices[0];
a.v1[y] = polygon_vertices[1];
a.v2[x] = polygon_vertices[index + 0];
a.v2[y] = polygon_vertices[index + 1];
a.v3[x] = polygon_vertices[index + 2];
a.v3[y] = polygon_vertices[index + 3];
triangle_area = area(a);
polygon_area += triangle_area;
}
printf("area=%.2f\t", polygon_area);
perim = perimeter(polygon_vertices, xycount);
printf("perimeter=%.2f\n", perim);
sprintf(result,"%.2f%.2f",polygon_area, perim);
if(strcmp(expected, result) == 0) {
printf("Arrays match.");
}
else{
printf("Arrays different\n");
};
}
fclose(data);
return 0;
}
/* calculate triangle area with Heron's formula */
double area(triangle a)
{
double s1, s2, s3, S, area;
s1 = side(a.v1, a.v2);
s2 = side(a.v2, a.v3);
s3 = side(a.v3, a.v1);
S = (s1 + s2 + s3) / 2;
area = sqrt(S*(S - s1)*(S - s2)*(S - s3));
return area;
}
/* calculate polygon perimeter */
double perimeter(double *vertices, int size)
{
int idx, jdx;
double p1[2], p2[2], pfirst[2], plast[2];
double perimeter;
perimeter = 0.0;
/* 1st vertex of the polygon */
pfirst[x] = vertices[0];
pfirst[y] = vertices[1];
/* last vertex of polygon */
plast[x] = vertices[size-2];
plast[y] = vertices[size-1];
/* calculate perimeter minus last side */
for(idx = 0; idx <= size-3; idx += 2)
{
for(jdx = 0; jdx < 4; ++jdx)
{
p1[x] = vertices[idx];
p1[y] = vertices[idx+1];
p2[x] = vertices[idx+2];
p2[y] = vertices[idx+3];
}
perimeter += side(p1, p2);
}
/* add last side */
perimeter += side(plast, pfirst);
return perimeter;
}
/* calculate length of side */
double side(double *p1, double *p2)
{
double s1, s2, s3;
s1 = (p1[x] - p2[x]);
s2 = (p1[y] - p2[y]);
s3 = (s1 * s1) + (s2 * s2);
return sqrt(s3);
}