View Compilation Error

0_0_2021368_15357.cpp: In function `void add()':
0_0_2021368_15357.cpp:11: error: invalid operands of types `char[20]' and `char[20]' to binary `operator+'
0_0_2021368_15357.cpp:18: error: name lookup of `i' changed for new ISO `for' scoping
0_0_2021368_15357.cpp:9: error:   using obsolete binding at `i'
0_0_2021368_15357.cpp:28: error: `strrev' undeclared (first use this function)
0_0_2021368_15357.cpp:28: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2021368_15357.cpp: In function `int main()':
0_0_2021368_15357.cpp:46: error: `strrev' undeclared (first use this function)