View Compilation Error

0_0_19869376_13348.c: In function 'main':
0_0_19869376_13348.c:9:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for(int i=0;i<=len;i++)
  ^
0_0_19869376_13348.c:9:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_19869376_13348.c:43:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for(int a=0;a<n;a++)
  ^