The algorithm inverse number

Question

Is this a formula for the inverse number?

eg 123-321?

Number is K

inv K= K%100 + K/10%10 * 10 + K % 10 *100

I'm not sure I exactly wrote, and I need this right for the task at school for graphic algorithm

Edit:Yes i'm stupid xD I'm Beginner xD

I would separate the calculations more to make them easier to follow, like `units = K %10; tens = ...; hundreds = ...;` and then when the digits are all separate, combine them again `inv = 100 * units + 10 * tens + hundreds;`. — Bo Persson, Jan 02 '17 at 19:22
You're not very clear as to what you're asking. Is `123-321` a string you receive and have to verify it's a palindrome? of you you receive `123` and have to return `321`? Will the numbers you receive always 3 digits long? — AntonH, Jan 02 '17 at 19:24
I do not need this to write a program, but I would draw an algorithm for the number of 3 digits. It is good way or not? my english is suck sorry xD — Nemanja Milenovic, Jan 02 '17 at 19:25
From a logic standpoint, what you wrote **looks** correct, but is a very specific solution to the problem. If you code it, you may have to be careful with operation precedence, though, so may need to add brackets for clarification. — AntonH, Jan 02 '17 at 19:30
Convert the number to a string (library function). Reverse the string. Convert that string to another number (library function) - but watch out for [octal](https://en.wikipedia.org/wiki/Octal) if a leading `0` is present! Then subtract the two numbers. — Weather Vane, Jan 02 '17 at 19:31
If you need to reverse a number, keep it as a string, then use methods to revers the string. — Thomas Matthews, Jan 02 '17 at 20:10
Yes, if you only need to print the reversed number and not to use it as a number, then it has sense to read and reverse directly as string. But do not **convert** it to string and back, because that is very wasteful compared to doing it directly in int (dynamic memory allocation for string etc.). — EmDroid, Jan 02 '17 at 20:17

score 3 · Answer 1 · answered Jan 02 '17 at 19:39

3

This logic will help you. variable inverse is the output.

        int num = 123;
        double inverse = 0;
        while (num != 0)
        {
            inverse = inverse * 10;
            inverse = inverse + num % 10;
            num = num / 10;                
        }

answered Jan 02 '17 at 19:39

Ankit Agarwal

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4

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Why type of `inverse` is `double` instead of `int` ? – J. Piquard Jan 02 '17 at 20:11
Thanks Mr. J. Piquard for your comment... It should be int. But there is no issue with double also. – Ankit Agarwal Jan 03 '17 at 16:09

score 1 · Answer 2 · answered Jan 02 '17 at 19:53

1

If you want your code to work with any number, consider converting to a string and then reversing it!

int invert( int input )
{
    std::stringstream str;
    str << input;

    std::string s = str.str();
    std::reverse(s.begin(),s.end());

    return atoi( s.c_str() );
}

answered Jan 02 '17 at 19:53

jpo38

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10
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I'd prefer to do it directly in integer instead of doing unnecessary conversions to/from string (involving dynamic memory allocations btw.). – EmDroid Jan 02 '17 at 20:06

Amjad · Answer 3 · 2017-01-02T20:10:07.873

0

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    int i = 123045 , j = 0,k=0;

    while( i != 0 )
        {
        j=i%10;
        k = k *10 + j;
        i /=10;
    }

    printf("%d\n", k);
    return 0;
}

Output 540321

edited Jan 02 '17 at 20:10

answered Jan 02 '17 at 19:42

Amjad

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2
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In each iteration of the while loop `i%10` will extract the first digit from right. This digit is carried over to `k` by `j` and we remove the digit from `i` by using integer division. – Amjad Jan 02 '17 at 19:46
2

This will not work for number containing zero, e.g. 12305, the termination condition is wrong. – EmDroid Jan 02 '17 at 20:03
Modified; Thanks for bringing this up! – Amjad Jan 02 '17 at 20:10

The algorithm inverse number

3 Answers3