Armstrong number using for loop in C++
What is For Loop?
A for loop is a repetitive control structure that allows you to create a loop to execute a specific number of times efficiently.
The syntax that can be used for the for loop in the C++ programming language is given below:
for (initialization statement; termination condition; increment or decrement statement (used for modifying value for further evaluation))
{
/* main body of the “for” loop */
}
Working of For Loop in C++
In for loop, the initialization command is implemented only once. After that, it checks the test expression of the loop and finds whether the test expression is false or true. And, for loop is dismissed if the test expression is false.
If the test expression of the 'F' loop becomes true, then the program line provided in the F loop’s body is executed, and the update expression is changed accordingly.
Again, the entire process of evaluation is to be done. The loop executes its body until and unless the value of the test expression in for loop becomes false.
The loop automatically terminates as soon as the test expression result becomes false.
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 For 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, a=0, b;
/* declaring various variables and initialization the value of 'a' as 0 */
cout<<"input any natural number that you want to check as Armstrong or not: ";
/* here we let user to enter a number via this program line */
cin>>n;
/* assigning the value entered by the user to variable 'n' */
for (b=n; n>0; n=n/10)
/* for (initialization statement; test expression or termination condition; increment or decrement statement) */
{
c=n % 10;
/* initializing assignment operator and assigning the value ‘n % 10’ to ‘c’ */
a=a+(c*c*c);
/* initializing assignment operator and assigning the value of ‘c*c*c’ to ‘a’ */
}
if(a==b)
/* 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"<< b;
/* printing the value of result as an output */
else // else statement
cout<<"The number %d, that you have entered is not an Armstrong number.\n"<< b;
/* printing the value of result as an output */
}
OUTPUT
Input any natural number that you want to check as Armstrong or not : 153
The number 153, that you have entered is an Armstrong numberEXPLANATION
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.
After that, we wrote a statement which will allow the user to enter the value for the variable ‘n’ with the ‘scanf’ command. The value in variable n holds that value which we want to test.
In the following line we initialized a ‘for’ 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 for loop, we initialized an if else statement and put the condition (a==n). 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 (153>0) here you can see the ‘for’ loop test expression is true,
b=n%10 (b=153%10) So, the remainder of n%10 is 3.
a=a +b*b*b (a = 0 +3*3*3) So, the value of a is 27.
n=n/10 (n=153/10) So, the value of n is 15.
2. n>0 (15>0) here you can see the for loop test expression is true,
b=n%10 (b=15%10) So, the remainder of n%10 is 5.
a=a +b*b*b (a = 27 +5*5*5) So the value of a is now 152.
n=n/10 (n=15/10) So the value of n is now 1.
3. n>0 (1>0) here you can see the for loop test expression is true,
b=n%10 (b=1%10) So, the remainder of n%10 is 1.
a=a +b*b*b (a = 152 +1*1*1) So, the value of a is now 153.
n=n/10 (n=1/10) So, the value of n is now 0.
4. n>0 (0>0) here you can see the for loop test expression becomes false. And, the program execution ends.