View Compilation Error

0_0_12895306_21987.cpp: In function `int main()':
0_0_12895306_21987.cpp:9: error: `strlen' undeclared (first use this function)
0_0_12895306_21987.cpp:9: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_12895306_21987.cpp:12: error: `swap' undeclared (first use this function)