What is the reason for these errors and how to fix it?

Question

C++ / C#

78 8 C:\Users\User\Desktop\1.c [Error] redefinition of 'file'
41 11 C:\Users\User\Desktop\1.c [Note] previous definition of 'file' was

here be?

#include <stdio.h>
#include <malloc.h>
#include <stdlib.h>
int main(){
  int l;
  int m = 0, n = 0
  , k = 0 
  , x = 0
  , i = 0, j = 0, w = 0;
  int** a; 
  l = getchar();
  switch(l)
  {
    case 'a':
    scanf("%d%d%d", &k, &n, &m);

  a = (int**)malloc(n * sizeof(int*));
  for (i = 0; i < n; i++) 
  {
    a[i] = (int*)malloc(m * sizeof(int));
    for (j = 0; j < m; j++) { a[i][j] = 0; }
  }

  for (w = 0; w < k; ++w)
  {
    for (i = 0; i < n; i++) 
    {
      for (j = 0; j<m; j++)
      {
        printf("a[%d][%d] = ", i, j);
        scanf("%d", &x); 
        a[i][j] += x; 
      }
    }
  }

  printf("\nsumm: \n");
    FILE* file = fopen("file.txt", "w");
    for (i = 0; i < n; i++) {
    	for (j = 0; j < m; j++) {
    fprintf(file, "%d %d ", i, j);
}
fclose(file);
}  
  
  
    return 0;
  case 'b':

   
   scanf("%d%d%d", &k, &n, &m);

  a = (int**)malloc(n * sizeof(int*));
  for (i = 0; i < n; i++) 
  {
    a[i] = (int*)malloc(m * sizeof(int)); 
    for (j = 0; j < m; j++) { a[i][j] = 0; } 
  }

  for (w = 0; w < k; ++w) 
  {
    for (i = 0; i < n; i++) //строки
    {
      for (j = 0; j<m; j++)
      {
        printf("a[%d][%d] = ", i, j);
        scanf("%d", &x); //считываем значение матрицы
        a[i][j] += x;
      }
          }
}
printf("\nsumm: \n");
  FILE* file = fopen("file.txt", "w");
    for (j = 0; j < n; j++) {
    	for (i = 0; i < m; i++) {
    fprintf(file, "%d %d ", i, j);
    }
    fclose(file);
    return 0;
}
}
}

Answer 1

The first message is redefining the file object. The second - the previous definition was here.
Usually such questions are illustrated with code.