Mo2

#define _CRT_SECURE_NO_WARNINGS

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

int main()
{

    // variables for reading the measurements from file
    FILE* fp;
    size_t len = 0;
    char resp;

    double x, y;

    // open the input file "messwerte.txt" for reading
    fp = fopen("polygon1.txt", "r");
    if (fp == NULL)
    {
        // if file could not be opened (wrong path, not readable, ...)
        // output a short message and immediately exit
        printf("Eingabedatei kann nicht geoeffnet werden.\n");
        scanf("%c", &resp);
        exit(EXIT_FAILURE);
    }

    // print program header
    printf("\n\nProgramm zur Berechnung eines Polygons\n");
    printf("--------------------------------------------------------\n");

    // the following loop reads a new value in every iteration
    // until the end of the file or some invalid token is found
    int i = 1;
    int n = 0;
    double xarray[50];
    double yarray[50];


    while (1)
    {
        len = fscanf(fp, "%lf %lf", &x, &y);

        if (len == EOF)
            break;
        else if (len == 0) {
            printf("Unerwartetes Zeichen in der Eingabedatei.");
            scanf("%c", &resp);
            exit(EXIT_FAILURE);
        }

        xarray[i] = x;
        yarray[i] = y;

        printf("Lese Eckpunkt: %6.2f/%6.2f\n", x, y);
        i++;
        n++;
    }

    double sum = 0;
    double temp;

    i = 0;
    //if n= 4
    if (n == 4) {
        for (i = 1;i < n;i++) {

            temp = (yarray[i] + yarray[i + 1]) * (xarray[i] - xarray[i + 1]) / 2;

            printf("\nx = %.1f |x+1 = %.1f | y = %.1f |y+1 = %.1f | i = %d | temp = %.1f", xarray[i], xarray[i + 1], yarray[i], yarray[i + 1], i, temp);
            sum = sum + temp;
        }

    }

    //if n = 3 (xarray[1]-xarray[2])*(yarray[3]-yarray[2]
    if (n == 3) {

        sum = 0.5 * (xarray[2] - xarray[1]) * (yarray[3] - yarray[2]);


    }
    // output results
    printf("\nErgebnisse:\n");
    printf("-----------\n\n");
    printf("\nFlaecheninhalt = %.5f", sum);
    // finally close the input file and clean up memory
    fclose(fp);

    // wait for user input before closing terminal
    scanf("%c", &resp);
}