subscipher.c

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

int static cipher_ascii(const int character, const unsigned key_increment){
    if(character < 33 || character > 126){
        return character;
    }
    const int norm_character = character - 33;
    const int cipher_character = ((norm_character + key_increment) % 94) + 33;
    return cipher_character;
}

int static dcipher_ascii(const int chiper_character, const unsigned key_increment){
    if(chiper_character < 33 || chiper_character > 126){
        return chiper_character;
    }
    const int norm_character = chiper_character - 33;
    int character = norm_character - key_increment;
    character = character % 94;

    if(character < 0){
        character = 94 + character;
    }
    character += 33;
    return character;
}

int subs_cipher_ascii(const char *file_path, const unsigned key, const char *mode){
    FILE * input_file = fopen(file_path, "r");
    if(input_file == NULL){
        printf("Error reading the file\n");
        return EXIT_FAILURE;
    }

    int offset = 0;
    int bufsize = 2;
    char *output_text = malloc(bufsize);
    if(output_text == NULL){
        printf("Allocation error\n");
        return EXIT_FAILURE;
    }

    char character;
    while((character = fgetc(input_file)) != EOF){
        char cipher_char;
        if(strcmp(mode, "cipher") == 0){
            cipher_char = cipher_ascii(character, key);
        } else {
            cipher_char = dcipher_ascii(character, key);
        }
        if(offset == bufsize - 1){
            bufsize *= 2;
            char *new_buf = realloc(output_text, bufsize);
            if(new_buf == NULL){
                printf("Reallocation error\n");
                free(output_text);
                return EXIT_FAILURE;
            }
            output_text = new_buf;
        }
        output_text[offset++] = cipher_char;
    }
    fclose(input_file);

    if(offset < bufsize - 1){
        char *new_buf = realloc(output_text, offset + 1);
        if(new_buf == NULL){
            printf("Reallocation error\n");
            free(output_text);
            return EXIT_FAILURE;
        }
        output_text = new_buf;
    }

    FILE *output_file;
    if(strcmp(mode, "cipher") == 0){
        output_file = fopen("out.txt", "w");
        fputs(output_text, output_file);
        fclose(output_file);
    } else {
        output_file = fopen("dout.txt", "w");
        fputs(output_text, output_file);
        fclose(output_file);
    }

    return 0;
}