# C++ Programming Code Examples

## C++ > Computer Graphics Code Examples

### C++ Program to Represent Graph Using 2D Arrays

/* C++ Program to Represent Graph Using 2D Arrays - This algorithm represents a graph using 2D arrays. - This method of representing graphs is not efficient. - The time complexity of this algorithm is O(v*v). - This algorithm takes the input of the number of vertex and edges. - Take the input of connected vertex pairs. - Print the graph using 2D arrays. - Exit. */ #include<iostream> #include<iomanip> using namespace std; // A function to print the matrix. void PrintMat(int **mat, int n) { int i, j; cout<<"\n\n"<<setw(4)<<""; for(i = 0; i < n; i++) cout<<setw(3)<<"("<<i+1<<")"; cout<<"\n\n"; // Print 1 if the corresponding vertexes are connected otherwise 0. for(i = 0; i < n; i++) { cout<<setw(3)<<"("<<i+1<<")"; for(j = 0; j < n; j++) { cout<<setw(4)<<mat[i][j]; } cout<<"\n\n"; } } int main() { int i, v, e, j, v1, v2; // take the input of the number of edges. cout<<"Enter the number of vertexes of the graph: "; cin>>v; // Dynamically declare graph. int **graph; graph = new int*[v]; for(i = 0; i < v; i++) { graph[i] = new int[v]; for(j = 0; j < v; j++)graph[i][j] = 0; } cout<<"\nEnter the number of edges of the graph: "; cin>>e; // Take the input of the adjacent vertex pairs of the given graph. for(i = 0; i < e; i++) { cout<<"\nEnter the vertex pair for edge "<<i+1; cout<<"\nV(1): "; cin>>v1; cout<<"V(2): "; cin>>v2; graph[v1-1][v2-1] = 1; graph[v2-1][v1-1] = 1; } // Print the 2D array representation of the graph. PrintMat(graph, v); }

Allocate storage space. Default allocation functions (single-object form). A new operator is used to create the object while a delete operator is used to delete the object. When the object is created by using the new operator, then the object will exist until we explicitly use the delete operator to delete the object. Therefore, we can say that the lifetime of the object is not related to the block structure of the program.

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.

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.

The cout is a predefined object of ostream class. It is connected with the standard output device, which is usually a display screen. The cout is used in conjunction with stream insertion operator (<<) to display the output on a console. On most program environments, the standard output by default is the screen, and the C++ stream object defined to access it is cout. The "c" in cout refers to "character" and "out" means "output". Hence cout means "character output". The cout object is used along with the insertion operator << in order to display a stream of characters.

An array is defined as the collection of similar type of data items stored at contiguous memory locations. Arrays are the derived data type in C++ programming language which can store the primitive type of data such as int, char, double, float, etc. It also has the capability to store the collection of derived data types, such as pointers, structure, etc. The array is the simplest data structure where each data element can be randomly accessed by using its index number. C++ array is beneficial if you have to store similar elements. For example, if we want to store the marks of a student in 6 subjects, then we don't need to define different variables for the marks in the different subject. Instead of that, we can define an array which can store the marks in each subject at the contiguous memory locations.

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).

#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.

Set field width. Sets the field width to be used on output operations. The C++ function std::setw behaves as if member width were called with n as argument on the stream on which it is inserted/extracted as a manipulator (it can be inserted/extracted on input streams or output streams). It is used to sets the field width to be used on output operations. This manipulator is declared in header <iomanip>. This method accepts n as a parameter which is the integer argument corresponding to which the field width is to be set. This function returns an object of unspecified type. The setw function should only be used as a stream manipulator.

Problem takes E edges as input and outputs vertex cover of the graph, implementing the following heuristic. There is no "Polynomial" time algorithm "invented up to date" to find