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C++ > Strings Code Examples

Program to Implement Affine Cipher

/* Program to Implement Affine Cipher This is a C++ Program to implement Affine Cipher. The affine cipher is a type of monoalphabetic substitution cipher, wherein each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter. The formula used means that each letter encrypts to one other letter, and back again, meaning the cipher is essentially a standard substitution cipher with a rule governing which letter goes to which. As such, it has the weaknesses of all substitution ciphers. Each letter is enciphered with the function (ax+b)mod(26), where b is the magnitude of the shift. */ #include<iostream> #include<string.h> #include<stdlib.h> using namespace std; string encryptionMessage(string Msg) { string CTxt = ""; int a = 3; int b = 6; for (int i = 0; i < Msg.length(); i++) { CTxt = CTxt + (char) ((((a * Msg[i]) + b) % 26) + 65); } return CTxt; } string decryptionMessage(string CTxt) { string Msg = ""; int a = 3; int b = 6; int a_inv = 0; int flag = 0; for (int i = 0; i < 26; i++) { flag = (a * i) % 26; if (flag == 1) { a_inv = i; } } for (int i = 0; i < CTxt.length(); i++) { Msg = Msg + (char) (((a_inv * ((CTxt[i] - b)) % 26)) + 65); } return Msg; } int main(int argc, char **argv) { cout << "Enter the message: "; string message; cin >> message; cout << "Message is :" << message; cout << "\nEncrypted Message is : " << encryptionMessage(message); cout << "\nDecrypted Message is: " << decryptionMessage( encryptionMessage(message)); }

The cin object is used to accept input from the standard input device i.e. keyboard. It is defined in the iostream header file. C++ cin statement is the instance of the class istream and is used to read input from the standard input device which is usually a keyboard. The extraction operator(>>) is used along with the object cin for reading inputs. The extraction operator extracts the data from the object cin which is entered using the keyboard. The "c" in cin refers to "character" and "in" means "input". Hence cin means "character input". The cin object is used along with the extraction operator >> in order to receive a stream of characters.

A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.

Return length of string. Returns the length of the string, in terms of bytes. This function is used to find the length of the string in terms of bytes. This is the actual number of bytes that conform the contents of the string , which is not necessarily equal to the storage capacity. This is the number of actual bytes that conform the contents of the string, which is not necessarily equal to its storage capacity. Note that string objects handle bytes without knowledge of the encoding that may eventually be used to encode the characters it contains. Therefore, the value returned may not correspond to the actual number of encoded characters in sequences of multi-byte or variable-length characters (such as UTF-8).

In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement, The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.

Strings are objects that represent sequences of characters. The standard string class provides support for such objects with an interface similar to that of a standard container of bytes, but adding features specifically designed to operate with strings of single-byte characters. The string class is an instantiation of the basic_string class template that uses char (i.e., bytes) as its character type, with its default char_traits and allocator types. Note that this class handles bytes independently of the encoding used: If used to handle sequences of multi-byte or variable-length characters (such as UTF-8), all members of this class (such as length or size), as well as its iterators, will still operate in terms of bytes (not actual encoded characters).

#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.

Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code.

In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.

C++ program performs Naive string matching without using any specific library functions. A text and a pattern is given as input. Pattern is 'searched' for in the text and all "instances" of