View Compilation Error

0_0_22133248_2774.cpp: In function 'bool KMP(std::string, std::string)':
0_0_22133248_2774.cpp:24:19: error: expected ')' before 'j'
  while (i < len1  j < len2) {
                   ^
0_0_22133248_2774.cpp:24:27: error: expected ';' before ')' token
  while (i < len1  j < len2) {
                           ^