View Compilation Error

0_0_21961088_7695.c:4:6: error: variably modified 'str' at file scope
 char str[MAXN];
      ^
0_0_21961088_7695.c: In function 'main':
0_0_21961088_7695.c:14:9: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
         for(int i=0;i<len;i++)
         ^
0_0_21961088_7695.c:14:9: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code