View Compilation Error

0_0_23996583_8476.cpp: In function 'void kmp(char*, char*)':
0_0_23996583_8476.cpp:18:2: error: 'n' was not declared in this scope
  n = strlen(a);
  ^
0_0_23996583_8476.cpp:19:2: error: 'm' was not declared in this scope
  m = strlen(b);//提前写俩变量 m n ，而不是在下面循环的地方疯狂写strlen，不然每次都要算一遍效率低 
  ^