Question

I want to change this C code so that instead of prompting the user to enter the argument value, or requiring the argument be entered after by pressing the “enter” key, instead I want the code changed so that the program opens a file, (which include the input values) read in the elements and pass in the  input file as a command line argument. (the input file includes the size of the matrix and the matrix values)
 
Here's an example of the input file

3
2.3 2.7 3.0
6.5 7.36 14.8
14.1 10.6 -5.2

(where 3 is the size of the matrix followed by the matrix values)

I want this input file to be passed as a command line argument and produce the output instead of prompting the user to enter it manually.
please change following code so that it does that. thank you.

*This is a program to display the
upper triangular matrix and lower triangular matrix
for any given matrix. The method used here is
LU decomposition method. This program works for matrices
of order equal to or below 10x10*/
#include<stdio.h>
int main()
{
    int size,row,column,ctr1,ctr2;
    printf("ENTER THE SIZE OF THE MATRIX(size<10)\n");
    scanf("%d",&size);
    float matrix[10][10];
    printf("ENTER THE MATRIX\n");
    for(row=0;row<size;row++)
        for(column=0;column<size;column++)
            scanf("%f",&matrix[row][column]);
    float lowertriangle[10][10];//matrices for lower and uppper triangle
    float uppertriangle[10][10];
    for(row=0;row<size;row++)
        for(column=0;column<size;column++)
            {
                if(row>column)//initialise all elements of lower triangle in upper triangular matrix as 0
                     uppertriangle[row][column]=0.0;
                if(row<column)//initialise all elements of upper triangle in lower triangular matix as 0
                    lowertriangle[row][column]=0.0;
                if(row==column)//initialise all diagonal elements of lower triangular matrix as 1
                    lowertriangle[row][column]=1.0;
            }
/*The algorithm used later is from the book Introduction to algorithms by Thomas Cormen.For a better understaning one can
read this text under chapter Matrix Operations. */
    for(ctr1=0;ctr1<size;ctr1++)
    {
        uppertriangle[ctr1][ctr1]=matrix[ctr1][ctr1];
            for(ctr2=ctr1+1;ctr2<size;ctr2++)
            {
                uppertriangle[ctr1][ctr2]=matrix[ctr1][ctr2];
                lowertriangle[ctr2][ctr1]=matrix[ctr2][ctr1]/uppertriangle[ctr1][ctr1];
            }
             for(row=ctr1+1;row<size;row++)
                for(column=ctr1+1;column<size;column++)
                    matrix[row][column]=matrix[row][column]-lowertriangle[row][ctr1]*uppertriangle[ctr1][column];
    }
    printf("UPPER TRIANGULAR MATRIX\n");
    for(row=0;row<size;row++)
    {//displays upper triangular matrix
        for(column=0;column<size;column++)
            printf("%.2f ",uppertriangle[row][column]);
        printf("\n");
    }
        printf("LOWER TRIANGULAR MATRIX\n");
    for(row=0;row<size;row++)
    {//displays lower triangular matrix
        for(column=0;column<size;column++)
            printf("%.2f ",lowertriangle[row][column]);
        printf("\n");
    }
    getch();
}

Answer 1

If you have any doubts, please give me comment...

/*This is a program to display the

upper triangular matrix and lower triangular matrix

for any given matrix. The method used here is

LU decomposition method. This program works for matrices

of order equal to or below 10x10*/

#include<stdio.h>

int main(int argc, char *argv[])

{

if(argc!=2){

printf("Usage: ./a.out in_file\n");

return -1;

}

FILE *fp;

fp = fopen(argv[1], "r");

if(fp==NULL){

printf("Unable to open file\n");

return -1;

}

int size,row,column,ctr1,ctr2;

// printf("ENTER THE SIZE OF THE MATRIX(size<10)\n");

fscanf(fp, "%d",&size);

float matrix[10][10];

// printf("ENTER THE MATRIX\n");

for(row=0;row<size;row++)

for(column=0;column<size;column++)

fscanf(fp, "%f",&matrix[row][column]);

fclose(fp);

float lowertriangle[10][10];//matrices for lower and uppper triangle

float uppertriangle[10][10];

for(row=0;row<size;row++)

for(column=0;column<size;column++)

{

if(row>column)//initialise all elements of lower triangle in upper triangular matrix as 0

uppertriangle[row][column]=0.0;

if(row<column)//initialise all elements of upper triangle in lower triangular matix as 0

lowertriangle[row][column]=0.0;

if(row==column)//initialise all diagonal elements of lower triangular matrix as 1

lowertriangle[row][column]=1.0;

}

/*The algorithm used later is from the book Introduction to algorithms by Thomas Cormen.For a better understaning one can

read this text under chapter Matrix Operations. */

for(ctr1=0;ctr1<size;ctr1++)

{

uppertriangle[ctr1][ctr1]=matrix[ctr1][ctr1];

for(ctr2=ctr1+1;ctr2<size;ctr2++)

{

uppertriangle[ctr1][ctr2]=matrix[ctr1][ctr2];

lowertriangle[ctr2][ctr1]=matrix[ctr2][ctr1]/uppertriangle[ctr1][ctr1];

}

for(row=ctr1+1;row<size;row++)

for(column=ctr1+1;column<size;column++)

matrix[row][column]=matrix[row][column]-lowertriangle[row][ctr1]*uppertriangle[ctr1][column];

}

printf("UPPER TRIANGULAR MATRIX\n");

for(row=0;row<size;row++)

{//displays upper triangular matrix

for(column=0;column<size;column++)

printf("%.2f ",uppertriangle[row][column]);

printf("\n");

}

printf("LOWER TRIANGULAR MATRIX\n");

for(row=0;row<size;row++)

{//displays lower triangular matrix

for(column=0;column<size;column++)

printf("%.2f ",lowertriangle[row][column]);

printf("\n");

}

getch();

}