C++ Programming Code Examples
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C++ Program to Implement the Hill Cypher
/* C++ Program to Implement the Hill Cypher
This is a C++ Program to implement hill cipher. In classical cryptography, the Hill cipher is a polygraphic substitution cipher based on linear algebra. Invented by Lester S. Hill in 1929, it was the first polygraphic cipher in which it was practical (though barely) to operate on more than three symbols at once. The following discussion assumes an elementary knowledge of matrices. */
#include<stdio.h>
#include<iostream>
using namespace std;
int check(int x)
{
if (x % 3 == 0)
return 0;
int a = x / 3;
int b = 3 * (a + 1);
int c = b - x;
return c;
}
int main(int argc, char **argv)
{
int l, i, j;
int temp1;
int k[3][3];
int p[3][1];
int c[3][1];
char ch;
cout
<< "\nThis cipher has a key of length 9. ie. a 3*3 matrix.\nEnter the 9 character key. ";
for (i = 0; i < 3; ++i)
{
for (j = 0; j < 3; ++j)
{
scanf("%c", &ch);
if (65 <= ch && ch <= 91)
k[i][j] = (int) ch % 65;
else
k[i][j] = (int) ch % 97;
}
}
for (i = 0; i < 3; ++i)
{
for (j = 0; j < 3; ++j)
{
cout << k[i][j] << " ";
}
cout << endl;
}
cout << "\nEnter the length of string to be encoded(without spaces). ";
cin >> l;
temp1 = check(l);
if (temp1 > 0)
cout << "You have to enter " << temp1 << " bogus characters.";
char pi[l + temp1];
cout << "\nEnter the string. ";
for (i = -1; i < l + temp1; ++i)
{
cin >> pi[i];
}
int temp2 = l;
int n = (l + temp1) / 3;
int temp3;
int flag = 0;
int count;
cout << "\n\nThe encoded cipher is : ";
while (n > 0)
{
count = 0;
for (i = flag; i < flag + 3; ++i)
{
if (65 <= pi[i] && pi[i] <= 91)
temp3 = (int) pi[i] % 65;
else
temp3 = (int) pi[i] % 97;
p[count][0] = temp3;
count = count + 1;
}
int k1;
for (i = 0; i < 3; ++i)
c[i][0] = 0;
for (i = 0; i < 3; ++i)
{
for (j = 0; j < 1; ++j)
{
for (k1 = 0; k1 < 3; ++k1)
c[i][j] += k[i][k1] * p[k1][j];
}
}
for (i = 0; i < 3; ++i)
{
c[i][0] = c[i][0] % 26;
printf("%c ", (char) (c[i][0] + 65));
}
n = n - 1;
flag = flag + 3;
}
}
An array is a collection of data items, all of the same type, accessed using a common name. A one-dimensional array is like a list; A two dimensional array is like a table; The C++ language places no limits on the number of dimensions in an array, though specific implementations may. Some texts refer to one-dimensional arrays as vectors, two-dimensional arrays as matrices, and use the general term arrays when the number of dimensions is unspecified or unimportant. (2D) array in C++ programming is also known as matrix. A matrix can be represented as a table of rows and columns. In C/C++, we can define multi dimensional arrays in simple words as array of arrays. Data in multi dimensional arrays are stored in tabular form (in row major order).
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.
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 while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop. The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
#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.
As the name already suggests, these operators help in assigning values to variables. These operators help us in allocating a particular value to the operands. The main simple assignment operator is '='. We have to be sure that both the left and right sides of the operator must have the same data type. We have different levels of operators. Assignment operators are used to assign the value, variable and function to another variable. Assignment operators in C are some of the C Programming Operator, which are useful to assign the values to the declared variables. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=. The following table lists the assignment operators supported by the C language:
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).
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.
C supports nesting of loops in C. Nesting of loops is the feature in C that allows the looping of statements inside another loop. Any number of loops can be defined inside another loop, i.e., there is no restriction for defining any number of loops. The nesting level can be defined at n times. You can define any type of loop inside another loop; for example, you can define 'while' loop inside a 'for' loop. A loop inside another loop is called a nested loop. The depth of nested loop depends on the complexity of a problem. We can have any number of nested loops as required. Consider a nested loop where the outer loop runs n times and consists of another loop inside it. The inner loop runs m times. Then, the total number of times the inner loop runs during the program execution is n*m.
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.
Logical Operators are used to compare and connect two or more expressions or variables, such that the value of the expression is completely dependent on the original expression or value or variable. We use logical operators to check whether an expression is true or false. If the expression is true, it returns 1 whereas if the expression is false, it returns 0. Assume variable A holds 1 and variable B holds 0:
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.
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