View Compilation Error

0_0_11285551_1697.cpp: In function `void calc(char*, char*)':
0_0_11285551_1697.cpp:4: error: `strlen' undeclared (first use this function)
0_0_11285551_1697.cpp:4: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_11285551_1697.cpp:8: error: `c' undeclared (first use this function)