C++ Programming Code Examples
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Implement the One Time Pad Algorithm
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/* Implement the One Time Pad Algorithm
This C++ program encodes any message using the technique of one time pad cipher technique. Input is not case sensitive and works only for all characters. White spaces are not ignored but are produced as random characters in the decoded message.
Note: Since the key is required for decryption, it is printed on stdout. However, it is not safe to make the key public. */
#include<iostream>
#include<vector>
#include<stdlib.h>
using namespace std;
void to_upper_case(vector<char>& text, int len)
{
for (int j = 0; j < len; j++)
{
if (text[j] >= 97 && text[j] <= 122)
text[j] -= 32;
}
}
void print_string(vector<char> text, int len)
{
for (int j = 0; j < len; j++)
{
cout << (char) (text[j] + 65);
}
cout << endl;
return;
}
size_t get_input(vector<char>& msg)
{
char a;
while (1)
{
a = getchar();
if (a == '\n')
break;
msg.push_back(a);
}
return msg.size();
}
int main()
{
vector<char> msg;
vector<char> enc_msg;
vector<char> dec_msg;
int *p;
int j;
size_t len;
cout << "Enter Message to Encrypt:";
len = get_input(msg);
to_upper_case(msg, len);
p = (int*) malloc(msg.size() * sizeof(int));
for (j = 0; j < len; j++)
{
p[j] = rand() % 26;
if (msg[j] >= 65 && msg[j] <= 90)
enc_msg.push_back((char) ((msg[j] - 65 + p[j]) % 26));
else if (msg[j] >= 97 && msg[j] <= 122)
enc_msg.push_back((char) ((msg[j] - 97 + p[j]) % 26));
else
enc_msg.push_back((char) msg[j]);
}
cout << "\nEncoded Message:";
print_string(enc_msg, len);
cout << "\nKey for decryption:\n";
for (j = 0; j < len; j++)
{
cout << (char) (p[j] + 65);
}
cout << endl;
cout << "\nDecrypted Message:";
for (j = 0; j < len; j++)
{
if ((enc_msg[j] - p[j]) < 0)
dec_msg.push_back((char) (enc_msg[j] - p[j] + 26));
else if ((enc_msg[j] - p[j]) >= 0)
dec_msg.push_back((char) (enc_msg[j] - p[j]));
else
dec_msg.push_back((char) enc_msg[j]);
}
print_string(dec_msg, len);
return 0;
}
Return size. Returns the number of elements in the vector. This is the number of actual objects held in the vector, which is not necessarily equal to its storage capacity. vector::size() is a library function of "vector" header, it is used to get the size of a vector, it returns the total number of elements in the vector. The dynamic array can be created by using a vector in C++. One or more elements can be inserted into or removed from the vector at the run time that increases or decreases the size of the vector. The size or length of the vector can be counted using any loop or the built-in function named size(). This function does not accept any parameter.
Break statement in C++ is a loop control statement defined using the break keyword. It is used to stop the current execution and proceed with the next one. When a compiler calls the break statement, it immediately stops the execution of the loop and transfers the control outside the loop and executes the other statements. In the case of a nested loop, break the statement stops the execution of the inner loop and proceeds with the outer loop. The statement itself says it breaks the loop. When the break statement is called in the program, it immediately terminates the loop and transfers the flow control to the statement mentioned outside the loop.
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.
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The sizeof() is an operator that evaluates the size of data type, constants, variable. It is a compile-time operator as it returns the size of any variable or a constant at the compilation time. The size, which is calculated by the sizeof() operator, is the amount of RAM occupied in the computer. The sizeof is a keyword, but it is a compile-time operator that determines the size, in bytes, of a variable or data type. The sizeof operator can be used to get the size of classes, structures, unions and any other user defined data type. The data_type can be the data type of the data, variables, constants, unions, structures, or any other user-defined data type.
Generate random number. Returns a pseudo-random integral number in the range between 0 and RAND_MAX. This number is generated by an algorithm that returns a sequence of apparently non-related numbers each time it is called. This algorithm uses a seed to generate the series, which should be initialized to some distinctive value using function srand. RAND_MAX is a constant defined in <cstdlib>. The rand() function in C++ is used to generate random numbers; it will generate the same number every time we run the program. In order to seed the rand() function, srand(unsigned int seed) is used. The srand() function sets the initial point for generating the pseudo-random numbers. The rand() function generates numbers randomly.
Put character. Inserts character c into the stream. Internally, the function accesses the output sequence by first constructing a sentry object. Then (if good), it inserts c into its associated stream buffer object as if calling its member function sputc, and finally destroys the sentry object before returning. Function returns the ostream object (*this).
Allocate memory block. Allocates a block of size bytes of memory, returning a pointer to the beginning of the block. The content of the newly allocated block of memory is not initialized, remaining with indeterminate values. If size is zero, the return value depends on the particular library implementation (it may or may not be a null pointer), but the returned pointer shall not be dereferenced. Malloc function in C++ is used to allocate a specified size of the block of memory dynamically uninitialized. It allocates the memory to the variable on the heap and returns the void pointer pointing to the beginning address of the memory block. The values in the memory block allocated remain uninitialized and indeterminate. In case the size specified in the function is zero then pointer returned must not be dereferenced as it can be a null pointer, and in this case, behavior depends on particular library implementation. When a memory block is allocated dynamically memory is allocated on the heap but the pointer is
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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Access element. Returns a reference to the element at position n in the vector container. A similar member function, vector::at, has the same behavior as this operator function, except that vector::at is bound-checked and signals if the requested position is out of range by throwing an out_of_range exception. Portable programs should never call this function with an argument n that is out of range, since this causes undefined behavior. Function returns the element at the specified position in the vector.
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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:
A function is like a black box. It takes in input, does something with it, and then spits out an answer. We have some "terminology" to refer to functions: A function, call it f, and that uses