det4

#include<stdio.h>
#include<stdlib.h>

int main(void)
{
  int n, i, j, ii, jj, row, col, result=0;
  int a[100][100];
  int b[10][10];
  
  printf("Input N = ");
  scanf("%d",&n);
  
  for(i=0; i < n ; i++) {
      for (j=0; j < n; j++) {
      printf("Input a%d,%d = ", i+1, j+1);
      scanf("%d",&a[i][j]);
    }
  }
  
  if ( n == 1 ) result = a[0][0];
  if ( n == 2 ) result = a[0][0]*a[1][1] - a[0][1]*a[1][0];
  if ( n == 3 ) result = a[0][0]*a[1][1]*a[2][2] + a[0][1]*a[1][2]*a[2][0] + a[0][2]*a[1][0]*a[2][1] - a[0][2]*a[1][1]*a[2][0] - a[0][0]*a[1][2]*a[2][1] - a[0][1]*a[1][0]*a[2][2];
      
  if ( n == 4 ) {
      // make subdet A0,0
      row=0; col=0;
      
      ii=0, jj=0;
      for( i=0; i<n; i++) {
          if (i == row) continue;
          for ( j=0; j<n; j++) {
              if (j == col) continue;
              b[ii][jj] = a[i][j];
              jj++; 
          }
          ii++; jj=0;
      }
      result +=  a[0][0] * ( b[0][0]*b[1][1]*b[2][2] + b[0][1]*b[1][2]*b[2][0] + b[0][2]*b[1][0]*b[2][1] - b[0][2]*b[1][1]*b[2][0] - b[0][0]*b[1][2]*b[2][1] - b[0][1]*b[1][0]*b[2][2] );
      // make subdet A1,0
      row=1; col=0;
      
      ii=0, jj=0;
      for( i=0; i<n; i++) {
          if (i == row) continue;
          for ( j=0; j<n; j++) {
              if (j == col) continue;
              b[ii][jj] = a[i][j];
              jj++; 
          }
          ii++; jj=0;
      }
      result -=  a[1][0] * ( b[0][0]*b[1][1]*b[2][2] + b[0][1]*b[1][2]*b[2][0] + b[0][2]*b[1][0]*b[2][1] - b[0][2]*b[1][1]*b[2][0] - b[0][0]*b[1][2]*b[2][1] - b[0][1]*b[1][0]*b[2][2] );
      // make subdet A2,0
      row=2; col=0;
      
      ii=0, jj=0;
      for( i=0; i<n; i++) {
          if (i == row) continue;
          for ( j=0; j<n; j++) {
              if (j == col) continue;
              b[ii][jj] = a[i][j];
              jj++; 
          }
          ii++; jj=0;
      }
      result += a[2][0] * ( b[0][0]*b[1][1]*b[2][2] + b[0][1]*b[1][2]*b[2][0] + b[0][2]*b[1][0]*b[2][1] - b[0][2]*b[1][1]*b[2][0] - b[0][0]*b[1][2]*b[2][1] - b[0][1]*b[1][0]*b[2][2] );
      // make subdet A3,0
      row=3; col=0;
      
      ii=0, jj=0;
      for( i=0; i<n; i++) {
          if (i == row) continue;
          for ( j=0; j<n; j++) {
              if (j == col) continue;
              b[ii][jj] = a[i][j];
              jj++; 
          }
          ii++; jj=0;
      }
      result -=  a[3][0] * ( b[0][0]*b[1][1]*b[2][2] + b[0][1]*b[1][2]*b[2][0] + b[0][2]*b[1][0]*b[2][1] - b[0][2]*b[1][1]*b[2][0] - b[0][0]*b[1][2]*b[2][1] - b[0][1]*b[1][0]*b[2][2] );
  }
  
  if ( n >=1 && n <= 4 ) {
      printf("det(A)=%d\n", result);
  } else {
      printf("Oh... I can't.");
  }
}