View Compilation Error

0_0_12151198_451.cpp: In function `void fun()':
0_0_12151198_451.cpp:47: error: `strrev' undeclared (first use this function)
0_0_12151198_451.cpp:47: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_12151198_451.cpp: At global scope:
0_0_12151198_451.cpp:69: error: `main' must return `int'