# C++ Programming Code Examples

## C++ > Algorithms Code Examples

### This program finds the locations of placing n queens in a n*n chessboard

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/* This program finds the locations of placing n queens in a n*n chessboard so that none attack any other */ #include<iostream.h> #include<conio.h> #include<math.h> #include<process.h> #include<graphics.h> class queen { int n,x[100]; public: queen(); void nqueen(int,int); int place(int,int); }; queen::queen() { int k=1; textcolor(GREEN); cprintf(" Enter the number of queens:"); cin>>n; nqueen( k, n); } void queen::nqueen(int k,int n) { for(int i=1;i<=n;i++) { if(place(k,i)) { x[k]=i; clrscr(); if(k==n) { for(int j=1;j<=n;j++) {textcolor(x[j]); gotoxy(1,j); cprintf(" queen %d : %d",j,x[j]); } getch(); break; } else nqueen(k+1,n); } } return; } int queen::place(int k,int i) { int j; for(j=1;j<=k;j++) { if((x[j]==i)||(abs(x[j]-i)==abs(j-k))) return 0; } return 1; } void main() { clrscr(); queen q; }

Absolute value. Returns the absolute value of parameter n ( /n/ ). In C++, this function is also overloaded in header <cmath> for floating-point types (see cmath abs), in header <complex> for complex numbers (see complex abs), and in header <valarray> for valarrays (see valarray abs). Basically the abs function evaluates the absolute value of the given value i.e. value after removing all the signs of negative and positive from the number. Which means it will always return a positive number. Function returns the absolute value of n. abs() function - In C the input is of type 'int' whereas in C++ input is of type 'int, long int or long long int'. In C the output is of 'int' type and in C++ the output has the same data type as input.

The getch() is a predefined non-standard function that is defined in conio.h header file. It is mostly used by the Dev C/C++, MS- DOS's compilers like Turbo C to hold the screen until the user passes a single value to exit from the console screen. It can also be used to read a single byte character or string from the keyboard and then print. It does not hold any parameters. It has no buffer area to store the input character in a program. The getch() function does not accept any parameter from the user. It returns the ASCII value of the key pressed by the user as an input.

Use the textcolor function to define what color you want to use for text. You can use this function to vary the text colors of your output. Colors must be written in all caps, or expressed as a numeral. Now, if you want your text to blink then while calling the textcolor() function pass the color and also say BLINK. This will like this: textcolor(BLUE+BLINK).

Positions cursor in text window. The gotoxy() function places the cursor at the desired location on the screen. This means it is possible to change the cursor location on the screen using the gotoxy() function. It is basically used to print text wherever the cursor is moved. If the coordinates are in any way invalid the call to gotoxy is ignored. Neither argument to gotoxy can be zero.

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.

It is a predefined function in "conio.h" (console input output header file) used to clear the console screen. It is a predefined function, by using this function we can clear the data from console (Monitor). Using of clrscr() is always optional but it should be place after variable or function declaration only. It is often used at the beginning of the program (mostly after variable declaration but not necessarily) so that the console is clear for our output.

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.

In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure. Constructors are special class functions which performs initialization of every object. The Compiler calls the Constructor whenever an object is created. Constructors initialize values to object members after storage is allocated to the object. Whereas, Destructor on the other hand is used to destroy the class object. • Default Constructor: A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.

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:

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.

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.

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 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 main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types. A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.

The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities. The if...else ladder allows you to check between multiple test expressions and execute different statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.

#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.

Here is the source code of the C++ program to "display the values" present in the nodes cyclically. C++ language sample displays the nodes of a "Doubly Linked List" with the last

A function or an entire class may be declared to be a friend of another class or function. A friend function can also be used for function overloading. Friend function declaration can

We can use "break" statement inside loops to terminate a 'loop & exit' it. In above example loop execution 'continues' until either n>=20 or entered score is negative. This statement

This C++ Program code example deals with all two-d transformation such as translation, 'scaling', 'rotation', 'reflection', 'shearing' in homogeneous coordinates. Transformation