View Compilation Error

0_0_30186540_29637.cpp: In function 'int change(std::string)':
0_0_30186540_29637.cpp:8:2: error: expected ',' or ';' before 'for'
  for(int i=0;i<=len;i++)
  ^
0_0_30186540_29637.cpp:8:14: error: 'i' was not declared in this scope
  for(int i=0;i<=len;i++)
              ^