Start args: key mode(encrypt/decrypt) input.txt output.txt OR input.txt output.txt (will encrypt and print the random key used)

encrypt_decrypt.c

#include<stdio.h>
#include<stdlib.h> //rand & srand
#include<time.h> //to seed srand


int main(int argc, char * argv[])
{
	FILE * file;
	long length; //file length
	char * text = 0;

	char mode = 'd'; //e = encryption, d = decryption
	int key;
	char * input;
	char * output;

	//(location),key,mode,input,output
	if (argc == 5) {

		sscanf_s(argv[1], "%d", &key);
		if (argv[2][0] == 'e' || argv[2][0] == 'E') mode = 'e'; //better than strcmp
		input = argv[3];
		output = argv[4];

	}
	//(location),input,output //this is encryption because you cant decrypt without a key anyways. Generates a random key.
	else if (argc == 3) {

		srand(time(NULL)); key = rand();
		mode = 'e';
		input = argv[1];
		output = argv[2];

	}
	else {
		printf("Wrong number of arguments. Must be either 4 or 2 (KMIO) or (IO)");
		return 2;
	}

	//read input
	fopen_s(&file, input, "r");
	if (!file) return 1;
	fseek(file, 0, SEEK_END);
	length = ftell(file);
	fseek(file, 0, SEEK_SET);
	text = malloc((length + 1) * sizeof(char));
	memset(text, 127, length + 1);
	if (text) fread(text, 1, length, file);
	fclose(file);

	//encrypt/decrypt
	if (text)
	{

		srand(key);

		for (int i = 0; i < (length + 1); i++) {

			int r = rand() % 97; // random
			char p = text[i]; //current char
			char p1 = 0; //new char

			if (mode == 'e') { //Encrypt

				if (p == '\t') p = 0;
				else if (p == '\n') p = 1;

				p1 = (p - 30)%99 + r;

			}
			else { //Decrypt

				p1 = (p + 30 - r);
				if (p1 == 0) p1 = '\t';
				if (p1 == 1) p1 = '\n';

			}

			text[i] = p1;
		}

		//write output
		fopen_s(&file, output, "w");
		if (!file) return 1;
		for (int i = 0; i < (length + 1); i++) {
			if (text[i] == 0 || text[i] > 126)break;
			fprintf(file, "%c", text[i]);
		}
		fclose(file);

	}

	printf("key:%d", key);

	//while(1){}

	return 0;
}

#include<stdio.h>
#include<stdlib.h> //rand & srand
#include<time.h> //to seed srand


int main(int argc, char * argv[])
{
	FILE * file;
	long length; //file length
	char * text = 0;

	char mode = 'd'; //e = encryption, d = decryption
	int key;
	char * input;
	char * output;

	//(location),key,mode,input,output
	if (argc == 5) {

		sscanf_s(argv[1], "%d", &key);
		if (argv[2][0] == 'e' || argv[2][0] == 'E') mode = 'e'; //better than strcmp
		input = argv[3];
		output = argv[4];

	}
	//(location),input,output //this is encryption because you cant decrypt without a key anyways. Generates a random key.
	else if (argc == 3) {

		srand(time(NULL)); key = rand();
		mode = 'e';
		input = argv[1];
		output = argv[2];

	}
	else {
		printf("Wrong number of arguments. Must be either 4 or 2 (KMIO) or (IO)");
		return 2;
	}

	//read input
	fopen_s(&file, input, "r");
	if (!file) return 1;
	fseek(file, 0, SEEK_END);
	length = ftell(file);
	fseek(file, 0, SEEK_SET);
	text = malloc((length + 1) * sizeof(char));
	memset(text, 127, length + 1);
	if (text) fread(text, 1, length, file);
	fclose(file);

	//encrypt/decrypt
	if (text)
	{

		srand(key);

		for (int i = 0; i < (length + 1); i++) {

			int r = rand() % 97; // random
			char p = text[i]; //current char
			char p1 = 0; //new char

			if (mode == 'e') { //Encrypt

				if (p == '\t') p = 0;
				else if (p == '\n') p = 1;

				p1 = (p - 30)%99 + r;

			}
			else { //Decrypt

				p1 = (p + 30 - r);
				if (p1 == 0) p1 = '\t';
				if (p1 == 1) p1 = '\n';

			}

			text[i] = p1;
		}

		//write output
		fopen_s(&file, output, "w");
		if (!file) return 1;
		for (int i = 0; i < (length + 1); i++) {
			if (text[i] == 0 || text[i] > 126)break;
			fprintf(file, "%c", text[i]);
		}
		fclose(file);

	}

	printf("key:%d", key);

	//while(1){}

	return 0;
}