/* Realize a function that receives as parameters a matrix and its dimension, i.e., the number of rows and columns.
   The function must change the sign of all the elements of the rows of the matrix that have an even row index
   (i.e, rows with indexes 0, 2, 4, 6,...). */

#include <stdio.h>

#define R 3
#define C 4

void change_sign(int matr[][C], int nr, int nc);

int main(){
  int m[R][C] = {{1, 2 , 3, 4}, {-1, -2, 3, 4}, {1, -2, 3, -4}};
  int i, j;

  printf("Initial matrix\n");
  for(i=0; i<R; i++){
    for(j=0; j<C; j++){
      printf("%3d", m[i][j]);
    }
    printf("\n");
  }

  change_sign(m, R, C);

  printf("Final matrix, with even index rows changed of sign\n");
  for(i=0; i<R; i++){
    for(j=0; j<C; j++){
      printf("%3d", m[i][j]);
    }
    printf("\n");
  }

  return 0;
}


void change_sign(int matr[][C], int nr, int nc){
  int r, c;
  
  for(r=0; r<nr; r++) {
    if(r%2==0) {
      for(c=0; c<nc; c++) {
        matr[r][c] = -1*matr[r][c];
      }
    }
  }
}