Debug assertion failed!

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <ctime>
#include <cstdio>
#include <conio.h>
 
#define N 20
 
int main()
{
    void view_file(FILE* file);
    srand(time(NULL));
    setlocale(LC_ALL, "rus");
    FILE *file1, *file2, *file3;
 
    file1 = fopen("file1.txt", "rt");
    file2 = fopen("file2.txt", "rt");
    file3 = fopen("file3.txt", "rt");
    double random;
    for (int i(0); i < N; ++i);
    {
        random = rand() % 100 + 101;
        fwrite(&random, sizeof(double), 1, file1);
        random = rand() % 100 + 1;
        fwrite(&random, sizeof(double), 1, file2);
 
    }
    rewind(file1);
    rewind(file2);
 
    int a, b, c;
    for (int i(0); i < N; ++i);
    {
        fwrite(&a, sizeof(double), 1, file1);
        fwrite(&b, sizeof(double), 1, file2);
        c = ((a / b) + 56) / (a + 5) ^ 2;
        fwrite(&c, sizeof(double), 1, file3);
    }
    rewind(file1);
    rewind(file2);
    rewind(file3);
 
    //std :: cout << std::endl << "First file: ";
    //view_file(file1); std::cout << std::endl;
    //std:: cout << std::endl << "Cesond file: ";
    //view_file(file2); std::cout << std::endl;
    //cout << endl << "Third file: ";
    
 
    _getch();
    return 0;
}

    fclose(file1);
    fclose(file2);
    fclose(file3);
 
    file1 = fopen("file1.txt", "rb");
    for (i=0; i < N; ++i)
    {
        fread(&a, sizeof(double), 1, file1);
        printf(" %lf\n",a);
    }
    fclose(file1);
    file2 = fopen("file2.txt", "rb");
    for (i=0; i < N; ++i)
    {
        fread(&a, sizeof(double), 1, file2);
        printf(" %lf\n",a);
    }
    fclose(file2);
    file3 = fopen("file3.txt", "rb");
    for (i=0; i < N; ++i)
    {
        fread(&a, sizeof(double), 1, file3);
        printf(" %lf\n",a);
    }
    fclose(file3);