CAESAR CPP DEC

// program to implement ceasar cipher decryption

#include <iostream>
#include <vector>
#include <algorithm>
#include <fstream>
#include <sstream>

using namespace std;

string decrypt(string original_msg, int shift_value){

    string allChars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ !\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~";
    int all_chars_length = allChars.length();


    string decrypted_msg = "";

    for(int i=0; i< original_msg.length(); i++){
        char letter = original_msg[i];
        int position = allChars.find(letter);
        if(position >= 0) {
            position -= shift_value;
            if(position < 0){
                position += all_chars_length;
            }
            position %= all_chars_length;
            char e_letter = allChars[position];
            decrypted_msg += e_letter;

}else{
            decrypted_msg += letter;
        }
    }


    return decrypted_msg;
}


static void decrypt_file(int shift_value){
    ifstream input_file;
    string file_name, data;
    cout<<"Enter File name : ";
    cin>>file_name;
    try {
        input_file.open(file_name);
        stringstream ss;
        ss << input_file.rdbuf();
        data = ss.str();
        cout<<"File read successufully!!"<<endl;
    } catch(exception e){
        cout<<e.what();
    }
    string decrypted_data = decrypt(data, shift_value);
    cout<<"File data decrypted successfully!!"<<endl;
    ofstream output_file;
    try {
        output_file.open("C:\\Users\\MOHIT\\Desktop\\ss.txt");
        output_file << decrypted_data;
        output_file.close();
        cout<<"decrypted file stored on Desktop!!"<<endl;
    }catch(exception ee){
        cout<<ee.what();
    }


}

int main()
{
    //cout << decrypt("My name is mohit, hello", 3) << endl;
    cout<<"Program to implement Ceasar Cipher"<<endl;
    cout<<"Enter shift value for decryption : ";
    int shift_value;
    cin>>shift_value;
    decrypt_file(shift_value);
}

/*
Output for decrypting a file
Program to implement Ceasar Cipher
Enter shift value for decryption : 3
Enter File name : F:/python_3.4/sample.txt
File read successufully!!
File data decrypted successfully!!
decrypted file stored on Desktop!!


 */