View Compilation Error

0_0_37564750_31998.cpp: In function 'int main()':
0_0_37564750_31998.cpp:9:21: error: 'strlen' was not declared in this scope
   int lena=strlen(s1);
                     ^
0_0_37564750_31998.cpp:11:18: error: 'strcmp' was not declared in this scope
   if(strcmp(s1,s2))cout<<"Equal"<<endl;
                  ^