View Compilation Error

0_0_17320440_22167.c: In function 'getNext':
0_0_17320440_22167.c:24:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for(int k=0;k<=len;k++)
  ^
0_0_17320440_22167.c:24:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code