C++ Loops
What is Loop?
A statement or a set of statements that is executed repeatedly is called loop. The statements in a loop are executed for a specified number of times or until some given condition remains true.
In C++, there are three kinds of loop statements. These are:
- The "while" loop
- The "for" loop
- The "do-while" loop
The "while" Loop
It is a conditional loop statement. It is used to execute a statement or a set of statement as long as the given condition remains true.
Syntax:
The syntax of the while loop is:
while (condition)
{
Statement;
}
where
condition: It consists of a relational expression. If it is true, the statement or the set of statement given in the while loop is executed.
statement: It represents the body of loop. The compound statements or a set of statements are written in braces {}.
Example:
Print "I Love Pakistan" five times using the "while" loop.
#include<iostream>
using namespace std;
int main()
{
int a=1;
while(a<=5)
{
cout<<"I Love Pakistan"<<"\n";
a=a+1;
}
}
Output:
Pakistan
Pakistan
Pakistan
Pakistan
Pakistan
Flowchart:
The "do-while" Loop
The do-while loop is also a conditional loop statement. It is like a while loop but in this loop the condition is tested after executing the statement of the loop.
Syntax:
The syntax of the do-while is:
do
{
statements;
}
while (condition);
where
do is a keyword of C++. It indicates the starting of the do-while loop.
statements statements enclosed in braces represent the body of loop.
condition it is the condition that must remain true for the execution of the loop.
Example:
Print first ten numbers by using do-while loop.
#include<iostream>
using namespace std;
int main()
{
int a;
a=1;
do
{
cout<<a<<"\n";
a++;
}
while(a<=10);
}
Output:
1
2
3
4
5
6
7
8
9
10
Flowchart:
The "for" Loop
The for loop statement is used to execute a set of statements repeatedly for a fixed number of times. It is also known as counter loop.
The structure of this loop is different from both the "while" and the "do-while" loops. It has the following parts:
- initialization
- condition
- increment or decrement
- body of the loop
Syntax:
The general syntax of the for loop is:
for (initialization; condition; increment/decrement)
Example:
Write a program to print first ten natural numbers using for loop.
#include<iostream>
using namespace std;
int main ()
{
int a;
for(a=1; a<=10; a++)
cout<<a<<"\n";
}
Flowchart:
Difference between while and do-while loop
while loop:
In while loop, test condition comes before the body of the loop. First the condition is tested and the then body of the loop is executed.
do-while loop:
In do-while loop, the body of the loop comes before the test condition. The body of the loop is executed and then the condition is tested.