View Compilation Error

0_0_38545816_4957.cpp: In function 'int main()':
0_0_38545816_4957.cpp:9:25: error: 'strlen' was not declared in this scope
      len[k] = strlen(arr);
                         ^
0_0_38545816_4957.cpp:13:30: error: invalid operands of types 'int [20]' and 'int' to binary 'operator/'
   for (int i = 0; i <= len / 2; i++)
                              ^