View Compilation Error

0_0_21187374_9067.cpp: In function 'int main()':
0_0_21187374_9067.cpp:15:23: error: 'strlen' was not declared in this scope
   int len_a = strlen(a),len_b = strlen(b);
                       ^
0_0_21187374_9067.cpp:16:23: error: 'len_b' was not declared in this scope
   int len = min(len_a,len_b);
                       ^