#include <bits/stdc++.h>
using namespace std;

string encrypt(string key, char mat[][3]) {
  int rows = sizeof(mat) / sizeof(mat[0]);
  int cols = sizeof(mat[0]) / sizeof(mat[0][0]);
  
  string result = "";
  for(int i=0; i < cols; i++) {
    int selCol = key[i]-'0'-1;
    for(int j = 0; j < 4; j++) {
      if(mat[j][selCol]==0) continue;
      result+=mat[j][selCol];
    }
  }
  
  return result;
}

void decrypt(string key, string cipher) {
  int rows = 4;
  int cols = 3;
  char mat[4][3];
  
  int i=0, k=0, m=0;
    
  while(k < cipher.length()) {
    int selCol = key[m]-'0'-1;
    cout<<selCol;
    mat[i][selCol] = cipher[k];
    k++;
    i++;
    if(i==rows) {
      i=0;
      m++;
    }
  }
  
  cout<<"\nPlain Text: ";
  for(int i=0; i < 4; i++) {
    for(int j=0; j < 3; j++) {
      // if(mat[i][j]==0) continue;
      cout<<mat[i][j];
    }
  }
}

int main() 
{
    string message = "HELLOWORLD";
    string key = "231";
    // char mat[ceil(message.length()/3)][key.length()]; // mat[3][3]
    char mat[4][3];
    
    cout<<"Message: "<<message<<endl;
    cout<<"Key: "<<key<<endl;
    
    int i=0, j=0, k=0;
    while(k < message.length()) {
      mat[i][j] = message[k];
      k++;
      j++;
      if(j==3) {
        j=0;
        i++;
      }
    }
    
    cout<<"Matrix: \n";
    for(int i=0; i < 4; i++) {
      for(int j=0; j < 3; j++) {
        cout<<mat[i][j]<<'\t';
      }
      cout<<endl;
    }
    
    cout<<"Cipher: ";
    string cipher = encrypt(key, mat);
    cout<<cipher;
    
    decrypt(key, cipher);
    
    return 0;
}
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C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}