Read file perform operation and output file in C

#include <stdio.h>

void main()

{

  int i,j;

  float A[3][3];

  float B[3][3];

  FILE *inputMatrix=fopen("filein.txt","r");

  for(i=0;i<3;++i){

     for(j=0;j<3;++j){

         fscanf(inputMatrix,"%f",&A[i][j]);

     }

  }

  fclose(inputMatrix);

//Operation

 for (i = 0; i < 3; i++)

    {

        for (j = 0; j < 3; j++)

        {

            B[i][j] = A[i][j] + A[i][j];

        }

    }

//write

   FILE *f;

   f = fopen("output.txt","w");

   for(i=0; i<3; i++)

    {

        for(j=0; j<3; j++)

        {

        fprintf(f,"\t %f",B[i][j]); 

        }

                fprintf(f,"\n"); 

       }

   fclose(f);

}