Armstrong Number using While Loop in C++
What is while Loop?
A while loop or while statement repeats all code of its body as long as a specific condition is satisfied. The loop ends if or when the condition no longer met.
The syntax that can be used for the “while” loop in the C++ programming language is following:
while(condition)
{
statement(x);
}
Working of While loop in C++
The test expression which is to be entered into the "while" loop is written between parentheses.
There are currently two options of test expression. If the expression is true, then the "while" loop will be executed automatically and the evaluation procedure will be repeated until the test expression is true. And, if the test expression becomes false then the "while" loop will be terminated and the entire "while" loop procedure will be abandoned.
What are Armstrong Numbers?
Armstrong numbers are those natural positive numbers which are equal to the sum of cubes of each digit.
For example
a b c d... = a*n + b*n + c*n + d*n
Following is the While loop program which test a number entered by the user as an input is Armstrong or not:
#include<iostream>
Using namespace std;
int main ()
{
int n, c, b, a = 0;
/* declaring various variables and initialization the value of 'a' as 0 */
cout<<"Input any natural number that you want to check whether it is an Armstrong number or not: "<<;
/* here we let user to enter a number via this program line */
Cin>>c;
/* assigning the value entered by the user to variable 'n' */
n=c;
/* initializing assignment operator and assigning the value ‘c’ to ‘n’ */
/* Loop to calculate the sum of the cubes of its digits */
while(n>0) /* while (test expression or termination condition) */
{
b=n % 10;
/* initializing assignment operator and assigning the value of ‘n %10’ to ‘b’ */
a=a +b*b*b;
/* initializing assignment operator and assigning the value of ‘a +b*b*b’ to ‘a’ */
n=n/10;
}
/* if else condition to print Armstrong or Not */
if (a ==c)
/* initializing an ‘equal to’ operator and putting the condition to check if the value of a is equal to b or not */
cout<<"The number %d, that you have entered is an Armstrong number.\n"<<c;
else // else statement
cout<<"The number %d, that you have entered is not an Armstrong number.\n"<<c;
/* printing the value of result as an output */
getch ();
}
Output
Input any natural number that you want to check whether it is an Armstrong number or not: 407
The number 407, that you have entered is an Armstrong number.
Explanation of above code:
Initially, we have declared four variables – n, a, b, c. Then, we initialized the value of variable ‘a’ as 0, it means the initial value of variable ‘a’ will be 0 so that we can avoid the value of variable ‘a’ from going into negative.
In the following line we initialized a ‘while’ loop with the test expression or termination condition (n>0) which means the value of the variable ‘n’ must always be more than 0.
After the while loop, we initialized an if else statement and put the condition (n=c). It means that, if the value of ‘n’ is equal to ‘c’, then the statement in the IF part execute. And, if the condition false, then the statement in the else part will print.
Here, you can see how the above code is execute:
1. n>0 (407>0) here you can see the ‘while’ loop test expression is true,
b=n%10 (b=407%10) So, the remainder of n%10 is 7.
a=a +b*b*b (a = 0 +7*7*7) So, the value of a is 343.
n=n/10 (n=407/10) So, the value of n is 40.
2. n>0 (40>0) here you can see the while loop test expression is true,
b=n%10 (b=40%10) So, the remainder of n%10 is 0.
a=a +b*b*b (a = 343 +0*0*0) So the value of a is now 343.
n=n/10 (n=40/10) So the value of n is now 4.
3. n>0 (4>0) here you can see the while loop test expression is true,
b=n%10 (b=4%10) So, the remainder of n%10 is 4.
a=a +b*b*b (a = 343 +4*4*4) So, the value of a is now 407.
n=n/10 (n=4/10) So, the value of n is now 0.
4. n>0 (0>0) here you can see the while loop test expression becomes false. And, the program execution ends.