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Solve system of equation by Gaussian elimination

Discussion in 'C++' started by Nadr, May 16, 2009.

  1. Nadr

    Nadr New Member

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    Introduction



    Code for solving system of equation by Gaussian elimination method. The Code is well commented and would not need any further explanation

    The code



    Code:
    #include <stdio.h>
    #include <conio.h>
    #define N 100
    
    /****************************************************************/
    /***** Gauss elimination method to solve system of equation *****/
    /****************************************************************/
    
    void main()
    {
    	float coeff[N][N+1]={{4,2,1,11},{2,3,4,20},{3,5,3,22},};
    	/* Co-efficient inputing variables */
    	int i,j,k;		/*	Loop variables */
    	int n=3;		/* Number of equations */
    	float pivot;	/* pivoting variables */
    	float sum;		/* Back substitution sum storing variable */
    	float x[N];		/* values of the variables i.e. x's */
    	char ch;		/* choice inputing variable */
    	do
    	{
    		printf("\nEnter the number of variables\n");
    		scanf("%d",&n);
    		for(i=0;i<n;i++)
    		{
    			for(j=0;j<n+1;j++)
    			{
    				printf("\nEnter %d row %d col element\n",i+1,j+1);
    				scanf("%f",&coeff[i][j]);
    			}
    		}
    		for(k=0;k<n;k++)
    		{
    			for(i=k+1;i<n;i++)
    			{
    				pivot=coeff[i][k]/coeff[k][k];
    				for(j=k;j<n+1;j++)
    					coeff[i][j]=coeff[i][j]-pivot*coeff[k][j];
    			}
    		}
    		x[n-1]=coeff[n-1][n]/coeff[n-1][n-1];
    		for(i=n-2;i>=0;i--)
    		{
    			sum=0;
    			for(j=i;j<n+1;j++)
    				sum=sum+coeff[i][j]*x[j];
    			x[i]=(coeff[i][n]-sum)/coeff[i][i];
    		}
    		for(i=0;i<n;i++)
    			printf("\nx%d = %g\n",i+1,x[i]);
    		printf("\nDo you wish to continue[y/n]\n");
    		fflush(stdin);
    		scanf("%c",&ch);
    	}while(ch=='y' || ch=='Y');
    	getch();
    }
    
    Post if you have any queries.
     
  2. kiddo

    kiddo New Member

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    What is the use of fflush(stdin)?
    can you explain for me?
    i don't really know about it,
    but I often seen it after the end of a loop.....

    nice....
     
  3. shabbir

    shabbir Administrator Staff Member

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    Flushes the input buffer
     
  4. kiddo

    kiddo New Member

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    yeah, I know about flushs the inputBuffer.
    But, what I want to ask, "Why we must flush the inputBuffer? Is it important?".
    Coz I couldn't answert that question before, when my friend asked me.

    ---------------------------------------------------
    Sorry if my English not that good:surprised
     
  5. shabbir

    shabbir Administrator Staff Member

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    At times the input buffer contains input for which some scanf /cin statements are skipped without asking for input and so its a god practice to flush it.
     
  6. shabbir

    shabbir Administrator Staff Member

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  7. imjames407

    imjames407 New Member

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    Oh my god it really great.What about Eular's law?
     
  8. JamC

    JamC New Member

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    shabbir,

    I would NOT nominate this for Article of the Month...
    Reason- Does not follow ANSI C-

    int main void

    Should there be a requirement as such- if you are going to nominate this..

    And
    Code:
       float coeff[N][N+1]={{4,2,1,11},{2,3,4,20},{3,5,3,22},};
    Not need...
     
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  9. SaswatPadhi

    SaswatPadhi ~ Б0ЯИ Τ0 С0δЭ ~

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    :iagree: +1 JamC.
     
  10. Nadr

    Nadr New Member

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    The code works in TurboC because my assignments wanted it to work in that compiler and that is the one used by my university and it does not matter if its nominated or not but my intentions were to share my code for members
     
  11. SaswatPadhi

    SaswatPadhi ~ Б0ЯИ Τ0 С0δЭ ~

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    It's a bad practice to use fflush(stdin) to flush the input stream.This method is UNPORTABLE, and hence should be avoided !
    It will compile fine, but it's behavior is undefined on many C compilers.
    But, it can be used safely with output stream.

    To flush input stream, we can define something like :
    Code:
    void my_fflush(FILE *pFile)
    {
          char c;
          while( ((c = fgetc(pFile)) != EOF) && (c != '\n') );
    }
    and call it like :
    Code:
    my_fflush(stdin);
    :)
     

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