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Impressed by small code :)

Subscriber360 (22)
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#include <stdio.h>
 
int main()
{
   int n,count=0,reverse = 0; 
   printf("Enter a number to reverse\n");
   scanf("%d", &n);
 
   while (n != 0)
   {
      reverse = reverse * 10; 
      reverse = reverse + n%10; 
      n       = n/10;
 
 /*How this Works: 
 forexample for 194

0 x 10 = 0
0+4 = 4
194/10 = 19

4 x 10 = 40
40 + 19%10 = 49
19/10 = 1

49 x10 = 490
410 + 1%10 = 491
1/10 = 0
*/
   }
   printf("Reverse of entered number is = %d\n", reverse); 
   return 0;
}

I am beginner, and i found this code on google,
that only give reverse output of number. I am
really impressed by how it works, this part;
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 while (n != 0)
   {
      reverse = reverse * 10; 
      reverse = reverse + n%10; 
      n       = n/10;
   }

Is it good maths or programming?
Last edited on
giblit (3750)
Why exactly are you multiplying by 10?

Nevermind just realized that reverse is of type int and not string.


Can't you simply do 
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while(n)
{
    reverse += n % 10 + '0';
    n /= 10;
}
Last edited on
LB (13399)
You literally copy-pasted an explanation for how it works, only to ask how it works. What still confuses you?

@giblit: Not sure what adding the integer value of '0' is supposed to do.
Last edited on
giblit (3750)
As I mentioned, I was thinking it was a string data type.

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#include <iostream>
#include <string>

int main()
{
    std::string reverse = "";
    int input = 194;
    
    while(input)
    {
        reverse += input % 10 + '0';
        input /= 10;
    }
    
    std::cout << reverse << std::endl;
    
    return 0;
}



Though, the easiest way would simply to do

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#include <iostream>
#include <string>

int main()
{
    std::string input = "194";
    
    std::string reverse(input.rbegin(), input.rend());
    
    std::cout << reverse << std::endl;
    
    return 0;
}
Subscriber360 (22)
@giblit
I know that "n=n/10" = "n /= 10;", i could do that to simplify, but my question is different.

btw your While loop doesn't make sense, and it won't work.

I have described that how it works, see comments in code.
Last edited on
LB (13399)
giblit wrote:
reverse += input % 10 + '0';
This blows my mind. I see it and alarm bells go off saying "that shouldn't compile", yet it does. Somehow you mastered the art of order of operations and implicit conversions in a way that I am too afraid to. I would have used parenthesis and an explicit cast...
Subscriber360 wrote:
btw your While loop doesn't make sense, and it won't work.
It does - http://ideone.com/ZcRpWw
Last edited on
Subscriber360 (22)
@giblit
Good Morning Mr.giblit its C not C++ :)

@LB
Check my question.
Is it good maths or programming?
LB (13399)
It's a combination of both. It takes advantage of integer division (programming) to re-arrange the digits (math).

Subscriber360 wrote:
Good Morning Mr.giblit its C not C++ :)
Well, this is a C++ forum...
Last edited on
Subscriber360 (22)
@LB
Good Morning to u too Sir :). Thanks Alot!
Actually its 9:30a.m here.
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