testing

Simple_Substitution/README.md

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+# Simple Substitution Cipher
+
+## Description
+A simple substitution cipher replaces each letter in the plaintext with another letter from the alphabet, based on a predetermined key.
+
+## How to Build
+1. Navigate to the `build` directory.
+2. Run `make` to compile the project.
+
+## How to Run
+1. After building, you will find an executable named `substitution_cipher` in the `build` directory.
+2. Run it using `./substitution_cipher`.
+
+## How to Clean
+- Run `make clean` in the `build` directory to remove all compiled files.

Simple_Substitution/build/Makefile

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+# Variables
+CC = gcc
+CFLAGS = -I../include -Wall -Wextra
+OBJDIR = ../obj
+SRCDIR = ../src
+BINDIR = ../build
+
+# Source files
+SOURCES = $(SRCDIR)/main.c $(SRCDIR)/substitution_cipher.c
+OBJECTS = $(OBJDIR)/main.o $(OBJDIR)/substitution_cipher.o
+
+# Build target
+TARGET = substitution_cipher
+
+# Rules
+all: $(BINDIR)/$(TARGET)
+
+$(BINDIR)/$(TARGET): $(OBJECTS)
+	$(CC) $(OBJECTS) -o $(BINDIR)/$(TARGET)
+
+$(OBJDIR)/%.o: $(SRCDIR)/%.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+clean:
+	rm -f $(OBJDIR)/*.o $(BINDIR)/$(TARGET)
+
+.PHONY: all clean
+

Simple_Substitution/include/substitution_cipher.h

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+#ifndef SUBSTITUTION_CIPHER_H
+#define SUBSTITUTION_CIPHER_H
+
+void substitution_encrypt(char *message, const char *key);
+void substitution_decrypt(char *message, const char *key);
+
+#endif // SUBSTITUTION_CIPHER_H

Simple_Substitution/src/main.c

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+#include "substitution_cipher.h"
+#include <stdio.h>
+#include <string.h>
+
+int main() {
+    char message[256];
+    char key[27] = "QWERTYUIOPLKJHGFDSAZXCVBNM";  // Simple substitution key
+
+    printf("Enter a message to encrypt: ");
+    fgets(message, sizeof(message), stdin);
+    message[strcspn(message, "\n")] = '\0';  // Remove the newline character
+
+    // Encrypt the message
+    substitution_encrypt(message, key);
+    printf("Encrypted message: %s\n", message);
+
+    // Decrypt the message to verify it works
+    substitution_decrypt(message, key);
+    printf("Decrypted message: %s\n", message);
+
+    return 0;
+}

Simple_Substitution/src/substitution_cipher.c

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+#include "substitution_cipher.h"
+#include <string.h>
+#include <ctype.h>  // for isalpha, toupper
+
+// Helper function to find the position of a character in the alphabet
+static int find_position(char c) {
+    c = toupper(c);
+    return c - 'A';
+}
+
+// Encrypt the message using the provided key
+void substitution_encrypt(char *message, const char *key) {
+    for (int i = 0; message[i] != '\0'; i++) {
+        if (isalpha(message[i])) {
+            int pos = find_position(message[i]);
+            //char base = isupper(message[i]) ? 'A' : 'a';
+            message[i] = isupper(message[i]) ? key[pos] : tolower(key[pos]);
+        }
+    }
+}
+
+// Decrypt the message using the provided key
+void substitution_decrypt(char *message, const char *key) {
+    char reverse_key[26];
+    for (int i = 0; i < 26; i++) {
+        reverse_key[key[i] - 'A'] = 'A' + i;
+    }
+
+    for (int i = 0; message[i] != '\0'; i++) {
+        if (isalpha(message[i])) {
+            int pos = find_position(message[i]);
+            //char base = isupper(message[i]) ? 'A' : 'a';
+            message[i] = isupper(message[i]) ? reverse_key[pos] : tolower(reverse_key[pos]);
+        }
+    }
+}