View Compilation Error

0_0_17706057_19326.c: In function 'prefix_count':
0_0_17706057_19326.c:37:11: error: redeclaration of 'i' with no linkage
  for (int i = 0; i < strlen(str); i++)
           ^
0_0_17706057_19326.c:35:6: note: previous declaration of 'i' was here
  int i, index;
      ^
0_0_17706057_19326.c:37:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for (int i = 0; i < strlen(str); i++)
  ^
0_0_17706057_19326.c:37:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_17706057_19326.c: In function 'main':
0_0_17706057_19326.c:55:2: error: expected expression before '/' token
  //freopen("in.txt", "r", stdin);
  ^