View Compilation Error

0_0_35990751_25184.cpp: In function 'void init()':
0_0_35990751_25184.cpp:12:26: error: 'strlen' was not declared in this scope
  for (i = 0; i < strlen(a); i++)
                          ^
0_0_35990751_25184.cpp: In function 'int manacher()':
0_0_35990751_25184.cpp:26:28: error: 'strlen' was not declared in this scope
  int ans = -1, n = strlen(b), maxlen = 0, index = 0;
                            ^
0_0_35990751_25184.cpp:28:7: error: 'maxlen' was not declared in this scope
   if (maxlen > i)
       ^
0_0_35990751_25184.cpp:29:26: error: 'index' was not declared in this scope
    p[i] = std::min(p[2 * index - i], maxlen - i);
                          ^
0_0_35990751_25184.cpp:34:7: error: 'maxlen' was not declared in this scope
   if (maxlen <= p[i])
       ^
0_0_35990751_25184.cpp:35:23: error: 'index' was not declared in this scope
    maxlen = p[i] + i, index = i;
                       ^