foo.c: In function 'main':
foo.c:7:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for (int i = 1; i < 8; i++)
  ^
foo.c:7:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code