int decrypt(int key){
    int c, i;
    char newc;
    printf("%d",key);
    FILE *file, *fp;
    file = fopen("mystery01.txt", "r");
    fp = fopen ("decrypt.txt", "w+");

    if (file == NULL){
        return 0;
    }
    while((c = fgetc(file)) != EOF){
        c = c - key;
        while (c < 0){
            c +=256;
            if (c > 0){
                break;
            }
        }
        fputc(c, fp);
    }
    return 0;
}