Write a program in C using function reverse () that inputs a number and returns the reverse of that number. Input 1234 output 4321

Question

1.00/5 (1 vote)

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I wrote this code->

#include<stdio.h>
int reverse(int a);
int main()
{ 
	int n;
	printf(" enter a number");
	scanf("%d", &n);
	printf(" the reverse of %d is %d " , n, reverse(n));
}
int reverse(int a)
{
	int rem;
	for (int a; a>0; a=a/10 )
	{
	rem= a%10;
	printf("%d", rem);
	}
}

There is no error in this code but the output is wrong, pls help me out with this.

What I have tried:

#include<stdio.h>
int reverse(int a);
int main()
{ 
	int n;
	printf(" enter a number");
	scanf("%d", &n);
	printf(" the reverse of %d is %d " , n, reverse(n));
}
int reverse(int a)
{
	int rem;
	for (int a; a>0; a=a/10 )
	{
	rem= a%10;
	printf("%d", rem);
	}
}

Posted 22-Feb-21 8:06am

Vaishnavi Gour

Updated 22-Feb-21 18:31pm

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jeron1 22-Feb-21 15:34pm

Does it compile? Your reverse() function is supposed to return an int, but it returns nothing.

3 solutions

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OriginalGriff · Answer 1 · 2021-02-22T08:29:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C#

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Rick York · Answer 2 · 2021-02-22T10:16:00

Solution 2

You are on the right track - the modulus operator will let you peel off the digits one by one. You need to take it one step farther. I suggest you keep a running total for the result. As a digit is extracted from the input value, add its value to the total. You will have to adjust the total before adding the new value to get the correct result but I will leave that part for you to figure out.

You are very close.

Posted 22-Feb-21 10:16am

Rick York

Comments

k5054 22-Feb-21 17:33pm

True, but what's the reverse of 1000? Using integer math you'd get back "1", which isn't really correct. If only there was a way to convert a number to a string, and reverse the string.

Rick York 22-Feb-21 18:43pm

It depends on whether they want the number reversed as a string or as a number. His approach appears to be doing it numerically as it is supposed to return an integer. This is obviously not correct textually.

Patrice T · Answer 3 · 2021-02-22T18:31:00

Quote:
There is no error in this code but the output is wrong

There is 3 levels with errors, first level is syntax error which the compiler tells you, second level is logical error where you get wrong answers, third level is misconception error where you don't fully understand what you have to do or have wrong expectations.

Quote:
what's the reverse of 1000? Using integer math you'd get back "1", which isn't really correct.

Since you deal with integers, 1 is the correct answer because 1000 reverse to 0001 which same value as 1.

Quote:
If only there was a way to convert a number to a string, and reverse the string.

In fact input is a string, and you asked to convert to integer with the "%d" in scan. Feel free to read the documentation for more details.

C++

int reverse(int a) // here you say that the function have an integer result
{
	int rem;
	for (int a; a>0; a=a/10 )
	{
	rem= a%10;
	printf("%d", rem);
	}
	// which imply a missing return of result here
}

Code that build the result is missing and you should remove the printf.

Write a program in C using function reverse () that inputs a number and returns the reverse of that number. Input 1234 output 4321

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