 # C++ Programming Code Examples

## C++ > Algorithms Code Examples

### Merge Sort

/* Merge Sort */ #include <iostream.h> int a; void merge(int,int,int); void merge_sort(int low,int high) { int mid; if(low<high) { mid=(low+high)/2; merge_sort(low,mid); merge_sort(mid+1,high); merge(low,mid,high); } } void merge(int low,int mid,int high) { int h,i,j,b,k; h=low; i=low; j=mid+1; while((h<=mid)&&(j<=high)) { if(a[h]<=a[j]) { b[i]=a[h]; h++; } else { b[i]=a[j]; j++; } i++; } if(h>mid) { for(k=j;k<=high;k++) { b[i]=a[k]; i++; } } else { for(k=h;k<=mid;k++) { b[i]=a[k]; i++; } } for(k=low;k<=high;k++) a[k]=b[k]; } void main() { int num,i; cout<<"***************************************************"<<endl; cout<<" MERGE SORT PROGRAM "<<endl; cout<<"*******************************************************"<<endl; cout<<endl<<endl; cout<<"Please Enter THE NUMBER OF ELEMENTS you want to sort [THEN PRESS ENTER]:"<<endl; cin>>num; cout<<endl; cout<<"Now, Please Enter the ( "<< num <<" ) numbers (ELEMENTS) [THEN PRESS ENTER]:"<<endl; for(i=1;i<=num;i++) { cin>>a[i] ; } merge_sort(1,num); cout<<endl; cout<<"So, the sorted list (using MERGE SORT) will be :"<<endl; cout<<endl<<endl; for(i=1;i<=num;i++) cout<<a[i]<<" "; cout<<endl<<endl<<endl<<endl; }

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.

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.

A predefined object of the class called iostream class is used to insert the new line characters while flushing the stream is called endl in C++. This endl is similar to \n which performs the functionality of inserting new line characters but it does not flush the stream whereas endl does the job of inserting the new line characters while flushing the stream. Hence the statement cout<<endl; will be equal to the statement cout<< '\n' << flush; meaning the new line character used along with flush explicitly becomes equivalent to the endl statement in C++.

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.

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.

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:

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.

#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.

Return true if "empty"; else false. Remove all items. Return position to prior to first. Return "first position". Insert x after "current iterator" position p. Return position that views. ListItr

The 'C++ program' tries to count alphabetical letters from d to n, but a break makes it stop when it encounters k: In a for statement, the 'break' can stop the counting when particular