fileio2.c

#include<stdio.h>
#include<stdlib.h> //exit()

int main()
{
    FILE* fo;
    FILE* fi;
    FILE* fo2;

    float A[10];
    float L[10] = { 1.7,2.3,4.6,7.8,1,2,3,4,5,6};
    float W[10] = { 5.2,4.1,1.6,6.8,7,8,9,0,9,8 };

    fopen_s(&fo, "I:\\test\\area.dat", "w"); //a - append

    if (fo == NULL)
    {
        printf("!Error, cannot open file!");
        exit(1);
    }

    for (int i = 0; i < 10; i++)
    {
        A[i] = L[i] * W[i];
        printf("%d L=%0.2f W=%0.2f A=%0.2f\n",i+1, L[i], W[i], A[i]);
        fprintf_s(fo, "%0.2f\n",A[i]);
    }

    fclose(fo);

    fopen_s(&fi, "I:\\test\\area.dat", "r"); //r - read

    if (fi == NULL)
    {
        printf("!Error, cannot open file!");
        exit(1);
    }

    float A2[20] = {};
    for (int u = 0; u < 20; u++)
    {
        A2[u] = -1;
    }


    float data = 0.0;
    int fstatus = 0;
    int index = 0;

    do {
        fstatus = fscanf_s(fi, "%f", &data); //success = 1 , fail = -1
        if (fstatus == 1)//OK
        {
            A2[index] = data;
            index++;
        }

    } while (fstatus != -1);
    fclose(fi);

    int h = 0;

    while(A2[h]!=-1)
    {
        printf("Read data from file is %f\n", A2[h]);
        h++;
    }




    return 0;
}