Caesar Cipher

/// Encryption Process

Begin
   For i = 0 to msg[i] != '\0'
      ch = msg[i]
   //encrypt for lowercase letter
      If (ch >= 'a' and ch <= 'z')
         ch = ch + key
         if (ch > 'z')
            ch = ch - 'z' + 'a' - 1
         done
         msg[i] = ch
   //encrypt for uppercase letter
      else if (ch >= 'A' and ch <= 'Z')
         ch = ch + key
         if (ch > 'Z')
            ch = ch - 'Z' + 'A' - 1
         done
         msg[i] = ch
      done
   done
   Print Encrypted message
End

/// Decryption Process

Begin
   For i = 0 to msg[i] != '\0'
      ch = msg[i]
   //decrypt for lowercase letter
      if(ch >= 'a' and ch <= 'z')
         ch = ch - key
         if (ch < 'a')
            ch = ch +'z' - 'a' + 1
      done
      msg[i] = ch
   //decrypt for uppercase letter
      else if (ch >= 'A' and ch <= 'Z')
         ch = ch + key
         if (ch < 'A')
            ch = ch + 'Z' - 'A' + 1
         done
         msg[i] = ch
      done
   done
   Print decrypted message
End

//// CODE///////
#include<iostream>
#include<string.h>
using namespace std;
int main() {
   cout<<"Enter the message:\n";
   char msg[100];
   cin.getline(msg,100); //take the message as input
   int i, j, length,choice,key;
   cout << "Enter key: ";
   cin >> key; //take the key as input
   length = strlen(msg);
   cout<<"Enter your choice \n1. Encryption \n2. Decryption \n";
   cin>>choice;
   if (choice==1) //for encryption{
      char ch;
      for(int i = 0; msg[i] != '\0'; ++i) {
         ch = msg[i];
         //encrypt for lowercase letter
         If (ch >= 'a' && ch <= 'z'){
            ch = ch + key;
            if (ch > 'z') {
               ch = ch - 'z' + 'a' - 1;
            }  
            msg[i] = ch;
         }
         //encrypt for uppercase letter
         else if (ch >= 'A' && ch <= 'Z'){
            ch = ch + key;
            if (ch > 'Z'){
               ch = ch - 'Z' + 'A' - 1;
            }
            msg[i] = ch;
         }
      }
      printf("Encrypted message: %s", msg);
   }
   else if (choice == 2) { //for decryption
      char ch;
      for(int i = 0; msg[i] != '\0'; ++i) {
         ch = msg[i];
         //decrypt for lowercase letter
         if(ch >= 'a' && ch <= 'z') {
            ch = ch - key;
            if(ch < 'a'){
               ch = ch + 'z' - 'a' + 1;
            }
            msg[i] = ch;
         }
         //decrypt for uppercase letter
         else if(ch >= 'A' && ch <= 'Z') {
            ch = ch - key;
            if(ch < 'A') {
               ch = ch + 'Z' - 'A' + 1;
            }
            msg[i] = ch;
         }
      }
      cout << "Decrypted message: " << msg;
   }
}