View Compilation Error

0_0_10240711_32433.cpp: In function `int main()':
0_0_10240711_32433.cpp:8: error: `fun' undeclared (first use this function)
0_0_10240711_32433.cpp:8: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_10240711_32433.cpp: In function `int fun(int, int)':
0_0_10240711_32433.cpp:16: error: `int fun(int, int)' used prior to declaration