 # C++ Programming Code Examples

## C++ > Arrays and Matrices Code Examples

### Program to Find kth Smallest Element by the Method of Partitioning the Array

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/* Program to Find kth Smallest Element by the Method of Partitioning the Array 1. Implement partitioning to find the Kth smallest number from a dataset of n element. 2. The time complexity of this algorithm is O(n*log(n)). 1. Take the input of the data set. 2. Use the partition algorithm. 3. As we place the pivot at the (k-1)th index it will be the kth smallest number. 3. Exit. */ #include<iostream> using namespace std; // Swapping two values. void swap(int *a, int *b) { int temp; temp = *a; *a = *b; *b = temp; } // Partitioning the array on the basis of values at high as pivot value. int CreatePartition(int a[], int low, int high) { int pivot, index, x; index = low; pivot = high; // Getting index of pivot. for(x=low; x < high; x++) { if(a[x] < a[pivot]) { swap(&a[x], &a[index]); index++; } } // Swapping value at high and at the index obtained. swap(&a[pivot], &a[index]); return index; } // Implementing Partition. int Partition(int a[], int low, int high, int k) { int pindex; if(low < high) { // Partitioning array using last element as a pivot. // Recursively implementing partitioning in the direction to place the pivot at (k-1)th pivot. pindex = CreatePartition(a, low, high); if(pindex == k-1) return k-1; else if(pindex > k-1) Partition(a, low, pindex-1, k); else Partition(a, pindex+1, high, k); } } int main() { int n, x, k, kk; cout<<"\nEnter the number of data element: "; cin>>n; int arr[n]; for(x = 0; x < n; x++) { cout<<"Enter element "<<x+1<<": "; cin>>arr[x]; } cout<<"\nEnter the k for the kth smallest element: "; cin>>k; kk = Partition(arr, 0, n-1, k); // Printing the result. cout<<"\nThe kth smallest element: "<<arr[kk]; return 0; }

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.

Partition range in two. Rearranges the elements from the range [first,last), in such a way that all the elements for which pred returns true precede all those for which it returns false. The iterator returned points to the first element of the second group. The relative ordering within each group is not necessarily the same as before the call. See stable_partition for a function with a similar behavior but with stable ordering within each group. The function shall not modify its argument. This can either be a function pointer or a function object. Function returns an iterator that points to the first element of the second group of elements (those for which pred returns false), or last if this group is empty.

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.

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.

Compute natural logarithm. Returns the natural logarithm of x. The natural logarithm is the base-e logarithm: the inverse of the natural exponential function (exp). For common (base-10) logarithms, see log10. The C/C++ library function double log(double x) returns the natural logarithm (base-e logarithm) of x. Function returns natural logarithm of x. If x is negative, it causes a domain error. If x is zero, it may cause a pole error (depending on the library implementation).

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.

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.

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.

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.

Operator is a symbol that is used to perform "mathematical" or "logical" manipulations. +, -, *, /, %, Addition, Subtraction, Division and Multiplication, Modulus, ++, -- Increment and

Method that implements the basic primality test. If witness doesn't return 1, n is definitely composite. Do this by computing a^i (mod n) and looking for "non-trivial" square roots of 1

C++ Program perform LU Decomposition of a matrix. LU decomposition factors a matrix as the product of a Lower Triangular Matrix and an upper 'triangular matrix'. Code sometimes

"Self-Organizing" List updates on the basis of 'last searched item'. The sequential searching approach is used. In general search, 80% time only specific 20% of data is accessed. Sample