a problem wilth C program
 

Hi friends...

I have a problem with some c codes and I think that you will be Capable to point it up for me.
However, I do not want anybody to post the correct and complete code to me .

I want to enter a string of numbers and the program will check whether the entered string forms a multiplicative identity n*n matrix which means all elements are zero except for the diagonal elements
For example, 3*3 multiplicative identity
1 0 0
0 1 0
0 0 1

I think but I am not pretty sure that the problem is from the outer for-loop. But still I cannot figure the error out and here is my code fragment written in C:
======================================================

#include <stdio.h>

#include <string.h>

int main()

{

    int size,track=0,i,j ,sum=0;

    char string[400];

    printf("Enter the size of the matrix: ");

    scanf("%d",&size);

    gets(string);

    printf("Enter the %d by %d matrix (in row-order) ",size,size);

    gets(string);

    printf("the matrix elements are = %s \n", string);   

//notice that the entered string should be Separated by single space only





        for(j=0;j<(2*size*size-1);j=(j+2*size-1)) //go row by row 

        {

                for (i=0;i<2*size;i=i+2)    //go value by value in a single row

                {                

                if (string[j]!=1 && j==track || string[j]!=0 && j !=track)

                        sum= sum;

                        



                else if ((string[j]==1 && j==track) || (string[j]==0 && j !=track))

                        sum++;

                }

              track++;

                

        }

        if (sum==(size*size) )

                printf("This matrix is   a multiplicative identity\n");

        else

                printf("This matrix is  not a multiplicative identity\n");

    return 0;

}

=========================================
thanks.
and Remember I do not want to see any complete structure of the solution

the_shark


<< moderator edit: added code tags: [code][/code] >>

Re: a problem wilth C program
 

The most obvious problem is that you're testing for 0 or 1 instead of '0' or '1'. Remember the the contents of your string are characters, not integers. You're also going about the problem in a complicated way, but because you don't want help with that part, I won't show you a simpler solution.

Re: a problem wilth C program
 

Hi Narue,

First of all, I would like to thank you for editing my post and making the code more readable.

Second of all, I did follow your suggestions as well as other modifications and now my program is working properly. :cool:

Third of all, I though my way to develop the problem idea was the only way to do so. However, since you are more expert than me, I understood that the problem can be solved in simpler way.

Can you write down the id :idea: ea of the other way?

Quick note:
I am a beginner in C.
So my knowledge includes pointers, functions, string, arrays, structures, loops and condition statements. :o

I hope that your solution will be within my knowledge-base. :cheesy:

Again, thanks for the cooperation.

Re: a problem wilth C program
 

use double dimensional array.

Re: a problem wilth C program
 

>Can you write down the idea of the other way?
Look carefully at the data. You have a 1 followed by 0's, then another 1 and the same amount of 0's. If you count the 0's then you'll see that it's N + 1 where N is the size of the matrix (ie. NxN, or 3x3).

To verify that the matrix is valid, you need all 0's except for the first, and every (N + 1)st beyond that. Those values must be 1. This gives you an immediate solution for counting the 1's:

size_t len = strlen ( s );

for ( i = 0; i < len; i += N + 1 ) {

  if ( s[i] != '1' )

    invalid();

}

Now the only problem is making sure that the other values are all 0. The simplest way to do this is a trivial loop:

for ( i = 0; i < len; i++ ) {

  if ( s[i] != '0' )

    invalid();

}

But because there are 1's, that won't work unless you make sure that the 1's won't be counted, or won't make a difference if they are. You're probably ahead of me by now, but consider this:

size_t len = strlen ( s );

for ( i = 0; i < len; i += N + 1 ) {

  if ( s[i] != '1' )

    invalid();

  s[i] = '0'; // Turn a 1 into a 0

}



for ( i = 0; i < len; i++ ) {

  if ( s[i] != '0' )

    invalid();

}

This solution is easy to understand, easy to verify, and has linear complexity.

Re: a problem wilth C program
 

ahhhhhhha

The solution is much easier than I thought; I'll try to practice such ideas in the future.

Thanks Narue and varunrathi. :)