// C++ program for the above approach

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

// encdec class with encrypt() and
// decrypt() member functions
class encdec {
	int key;

	// File name to be encrypt
	string file = "geeksforgeeks.txt";
	char c;

public:
	void encrypt();
	void decrypt();
};

// Definition of encryption function
void encdec::encrypt()
{
	// Key to be used for encryption
	cout << "key: ";
	cin >> key;

	// Input stream
	fstream fin, fout;

	// Open input file
	// ios::binary- reading file
	// character by character
	fin.open(file, fstream::in);
	fout.open("encrypt.txt", fstream::out);

	// Reading original file till
	// end of file
	while (fin >> noskipws >> c) {
		int temp = (c + key);

		// Write temp as char in
		// output file
		fout << (char)temp;
	}

	// Closing both files
	fin.close();
	fout.close();
}

// Definition of decryption function
void encdec::decrypt()
{
	cout << "key: ";
	cin >> key;
	fstream fin;
	fstream fout;
	fin.open("encrypt.txt", fstream::in);
	fout.open("decrypt.txt", fstream::out);

	while (fin >> noskipws >> c) {

		// Remove the key from the
		// character
		int temp = (c - key);
		fout << (char)temp;
	}

	fin.close();
	fout.close();
}

// Driver Code
int main()
{
	encdec enc;
	char c;
	cout << "\n";
	cout << "Enter Your Choice : -> \n";
	cout << "1. encrypt \n";
	cout << "2. decrypt \n";
	cin >> c;
	cin.ignore();

	switch (c) {
	case '1': {
		enc.encrypt();
		break;
	}
	case '2': {
		enc.decrypt();
		break;
	}
	}
}

C Language online compiler

Write, Run & Share C Language code online using OneCompiler's C online compiler for free. It's one of the robust, feature-rich online compilers for C language, running the latest C version which is C18. Getting started with the OneCompiler's C editor is really 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 editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.

#include <stdio.h>
int main()
{
    char name[50];
    printf("Enter name:");
    scanf("%s", name);
    printf("Hello %s \n" , name );
    return 0;
    
}

About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

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);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

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.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

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
}