worked

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define LEN 20


void code(char* argv2, char* argv3, int shift) {//шифровка
    FILE* f_ptr1;
    FILE* f_ptr2;
    f_ptr1 = fopen(argv2, "r");
    f_ptr2 = fopen(argv3, "w");
    fseek(f_ptr1, 0, SEEK_END);
    long size = ftell(f_ptr1) + 1;
    fseek(f_ptr1, 0, SEEK_SET);
    char* str = (char*)malloc(size);
    fgets(str, (int)size, f_ptr1);
    printf("%s\n", str);

    for (int i = 0; i < strlen(str); i++) {
        str[i] = str[i] + ((int)shift % 127);
        if (str[i] > 127) str[i] = 0 + (str[i] + 127) - 1;
    }
    printf("%s", str);


    fputs(str, f_ptr2);
    fclose(f_ptr1);
    fclose(f_ptr2);
}

void decode(char* argv2, char* argv3, int shift) {//дешифровка
    FILE* f_ptr2;
    f_ptr2 = fopen(argv2, "r+");
    fseek(f_ptr2, 0, SEEK_END);
    long size = ftell(f_ptr2) + 1;
    fseek(f_ptr2, 0, SEEK_SET);
    char* dop = (char*)malloc(size);
    fgets(dop, size, f_ptr2);
    printf("\n%s", dop);


    for (int i = 0; i < strlen(dop); i++) {
        dop[i] = dop[i] - ((int)shift % 127);
        if (dop[i] < 0) dop[i] = 127 - (0 - dop[i]) + 1;
    }

    printf("\n%s", dop);
    fclose(f_ptr2);
    f_ptr2 = fopen(argv3, "w");
    fputs(dop, f_ptr2);
    fclose(f_ptr2);
}


int main(int argc, char* argv[])
{
    char* type = argv[1];
    char* first = argv[2];
    char* second = argv[3];
    char* res = argv[4];
    int shift = atoi(res);//аргументы кмд

    if (*type == '1')
        code(first, second, shift);
    else if (*type == '0')
        decode(first, second, shift);
    else
        printf("Wrong command");
    return 0;
}