foo.c: In function 'main':
foo.c:6:7: error: 'for' loop initial declarations are only allowed in C99 mode
foo.c:6:7: note: use option -std=c99 or -std=gnu99 to compile your code
foo.c:8:13: error: redefinition of 'i'
foo.c:6:15: note: previous definition of 'i' was here
foo.c:8:5: error: 'for' loop initial declarations are only allowed in C99 mode