Simple C++ code to generate Armstrong numbers [closed] - c++

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Closed 10 years ago.
The following is my simple attempt at generating Armstrong numbers. But it only outputs "1". What might be wrong?
#include<stdio.h>
#include<conio.h>
#include<iostream.h>
int main()
{
clrscr();
int r;
long int num = 0, i, sum = 0, temp;
cout << "Enter the maximum limit to generate Armstrong number ";
cin >> num;
cout << "Following armstrong numbers are found from 1 to " << num << "\t \n";
for(i=1;i<=num;i++)
{
temp = i;
while( temp != 0 )
{
r = temp%10;
sum = sum + r*r*r;
temp = temp / 10;
}
if ( i == sum ) {
cout << i;
sum = 0;
}
}
getch();
return 0;
}

Answer 1

You need to always set sum = 0 inside the for-i-loop.

Answer 2

Armstrong numbers: n-digit numbers equal to sum of n-th powers of their digits.
From your code
sum = sum + r*r*r;
'r*r*r' isn't n'th power of the number.

Answer 3

The first thing is that you're assuming that n (as in the nth power) is always three (in your r*r*r). That's only true if your initial value has three digits (as with the 153 example).
You need to count the digits in your initial number to calculate n, and then replace your r*r*r with raising r to the nth power.
This doesn't explain why 153 isn't found, though. The reason for that is because you aren't reseting sum to zero unless you find a match. You need to reset it to zero whether you found a match or not.

Answer 4

you can calculate n using log:
n = log(i)+1
then calculate r^n correctly and use it in your summation: sum += r^n;. r*r*r is not the correct way of calculating it.

Answer 5

Your code only works with n=3 : sum = sum + r*r*r;
You must use the pow() function (http://www.codecogs.com/reference/c/math.h/pow.php) to compute powers. (Or create a custom one.)

Answer 6

To summarize the right, but partial answers:
// #include <math.h>
for (long int i = 1; i <= num; i++)
{
long int n = 0, sum = 0; // <--- here
long ing temp = i;
while ( temp != 0 )
{
++n;
temp /= 10;
}
temp = i;
while ( temp != 0 )
{
int r = temp%10;
sum += int(pow(double(r), n)); // <-- here
temp /= 10;
}
if ( i == sum )
{
cout << i;
sum = 0;
}
}

Answer 7

#Power-inside, I saw your code, its difficult to change your code and edit it, but I have written a similar code to generate Armstrong numbers in a given limit, and it works fine.
Here it is....
#include<iostream.h>
#include<conio.h>
class arm
{
int a;
public:
void display();
};
void arm::display()
{
cout<<"Enter any number to find armstrong numbers less than it";
cin>>a;
for(int i=a;i>=1;i--)
{
int d=i;
int b=i;
int c=i;
int count=0;
while(b!=0)
{
b=b/10;
count++;
}
int l,m;
m=0;
for(int k=1;k<=count;k++)
{
l=c%10;
c=c/10;
m=m+l*l*l;
}
if(d==m)
cout<<d<<"\t";
}
}
void main()
{
arm k;
k.display();
getch();
}