Thread: Erroneous answer in algorithm problem

Dear All,

I have written a program that finds the integer whose square is closest to but greater than the integer number input as data. But it is giving me an erroneous answer. My algorithm is:

1. Select a number which is half the input number.
2. Square it and check whether it satisfies our condition.
3. Subtract one and square it and check whether it satisfies our condition.
4. Repeat 2 and 3 iteratively until a solution is obtained.

Below is my code for the above problem.

Code:

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int main()
{
    int n,m,input,powm,pown;
    printf("Enter a number");
    scanf("%d",&input);
    m=input/2;
    n=m-1;
    powm=pow(m,2);
    pown=pow(n,2);
    if (powm>input)
    {
          if(pown>input)
          {
          m=m-1;
          n=n-1;
          powm=pow(m,2);
          pown=pow(n,2);
          }
    }
    
    printf("The integer whose square is closest to but greater than the input number input is %d",n);
    
    system("pause");
    return 0;
}

Thank you for your reply.

Thanks for your reply. The input is 9, the expected output is 4 and the incorrect output is 3.

Originally Posted by stahta01

Step 4 implies the use of a loop; likely a do/while or while loop.

Suggestion: State the input, the expected output, and the incorrect output from your program.

Tim S.

Below is my code...I am encountering an unexpected error. My code doesn't give any output after I enter 9 as input.

Code:

/*program finds an integer whose square is closest to but greater than the integer number input as data*/

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int main()
{
    int n,m,input,powm,pown;
    printf("Enter a number");
    scanf("%d",&input);
    m=input/2;
    n=m-1;
    powm=pow(m,2);
    pown=pow(n,2);
    while (powm>input)
    {
          while(pown>input)
          {
          m=m-1;
          n=n-1;
          powm=pow(m,2);
          pown=pow(n,2);
          }
    }
    
    printf("The integer whose square is closest to but greater than the input number input is %d",m);
    
    system("pause");
    return 0;
}

Originally Posted by Salem

Post your latest code, showing how you used a while loop.

Your algorythm doesn't work if you use integer calculation.
Say your input is 5
divided by 2 gives 2.
2 squared = 4 and that is already lower then 5.
Kurt

Let's put it that way. If you loop while m*m > input is the same as looping until m*m <= input

. I would like to read book that enables me to think algorithms...any suggestions?

Originally Posted by abhishekcoder

. I would like to read book that enables me to think algorithms...any suggestions?

"Programming Pearls" come recommended.
I read it very little at a time, in my spare time.
If you're mathematically inclined, you can always try the Knuth Books.

Thanks