C program to check armstrong number

Question

#include<stdio.h>
#include<math.h>
#define pow
int main()
{
    int num,num1,num2,n,q,sum=0,no_of_digits=0;
    printf("enter  a number\n");
    scanf("%d",&num);
    num1=num2=num; //storing the entered number in another variable 'num1'
    while (num!=0) //calclating and storing the number of digits in 'digit'
    {
        num=num/10; //dividing the number by 10. int data type ignores the decimal value, giving an integer
        no_of_digits++; 
    }
    while (num1!=0) 
    {
        n=num1%10; //taking one digit at a time in n
        q=pow(n,no_of_digits);//each digit^no. of digits
        sum=sum+q; // sum of all digit^no. of digits
        num1=num1/10;
        
    }
     printf("Sum of each digit^no. of digits =%d\n",sum);
     if (sum==num2)
        printf("%d is an armstrong number\n",num2);
     else
        printf("%d is NOT an armstrong number\n",num2);

  return 0;
}

MY output: Sum of each digit^no. of digits =9 370 is NOT an armstrong number

Also, if i don't add the #define pow line,i get the following error. /usr/bin/ld: /tmp/ccGBiCYH.o: in function main': 7.c:(.text+0xda): undefined reference to pow' collect2: error: ld returned 1 exit status

Please tell me what I'm doing wrong. I checked all the other values (num,num1,....) and they all are right. The 'pow' function doesn't seem to be working correctly.

For the undefined reference to pow, see for the millionth time https://stackoverflow.com/questions/8671366/undefined-reference-to-pow-and-floor What do you think `#define pow` does? As for the logic here: Are you sure your computations fit in `int`s? — gspr, Apr 16 '22 at 08:59
Your `#define pow` turns this: `q=pow(n,no_of_digits);` into this: `q=(n,no_of_digits);` which is synonymous with `q=no_of_digits;` so it is no wonder the answers were wrong. This is why we don't *guess*, especially when it comes to standard library functions. When it doubt, read the docs, see what headers contain formal declarations, and what *libraries* contain formal implementations, including the former and linking the latter respectively. And I concur with others; don't think to be using floating-point here regardless. — WhozCraig, Apr 16 '22 at 09:11
Abh_03, to count the number of digits, do you consider 0 to have one or zero digits? Code here calculates zero. — chux - Reinstate Monica, Apr 16 '22 at 09:54
Ref: [Armstrong number](https://en.wikipedia.org/wiki/Narcissistic_number#C). — chux - Reinstate Monica, Apr 16 '22 at 09:58
Does this answer your question? [Undefined reference to \`pow' and \`floor'](https://stackoverflow.com/questions/8671366/undefined-reference-to-pow-and-floor) — hyde, Apr 16 '22 at 10:17

score 0 · Answer 1 · answered Apr 16 '22 at 11:26

It's required to give a definition for macro. When you write #define something, you'll have to define what it will do in your code.

A macro in C is a set of program statements that is replaced by the value of the macro throughout the entire program.

In your code, you wanted to write a macro for the power function.

So what a power function does?

It takes the base and exponent as parameters, then returns base ^ exponent.

You've to define this functionality in the macro. This is called Function-like Macros.

I would suggest learning more about macros before moving forward with it.

Let's get back to your code.

If you write a proper power function, I think your code will give the correct output.

Note: In case of both base and exponent being integer, it is safer to write your own integer power function.

Reason: Strange behavior of the pow function

Here I'm giving a sample code with a very basic approach of writing a power method.

#include<stdio.h>
#include<math.h>

int _power(int base,int exponent)
{
    int result = 1;
    for(int i = 1; i <= exponent; i++) result *= base;
    return result;
}

int main()
{
    int num,num1,num2,n,q,sum=0,no_of_digits=0;
    printf("enter  a number\n");
    scanf("%d",&num);
    num1=num2=num; //storing the entered number in another variable 'num1'
    while (num!=0) //calclating and storing the number of digits in 'digit'
    {
        num=num/10; //dividing the number by 10. int data type ignores the decimal value, giving an integer
        no_of_digits++;
    }
    while (num1!=0)
    {
        n=num1%10; //taking one digit at a time in n
        q=_power(n,no_of_digits);//each digit^no. of digits
        printf("n: %d   no_of_digits: %d    q: %d\n", n, no_of_digits, q);
        sum=sum+q; // sum of all digit^no. of digits
        printf("Sum: %d\n", sum);
        num1=num1/10;

    }
    printf("Sum of each digit^no. of digits =%d\n",sum);
    if (sum==num2)
        printf("%d is an armstrong number\n",num2);
    else
        printf("%d is NOT an armstrong number\n",num2);

    return 0;
}

Please check out the following resources to learn more about Macros and pow function

C program to check armstrong number

1 Answers1