View Compilation Error

125874_0_15748.cpp: In function `int mul()':
125874_0_15748.cpp:105: error: `plus' undeclared (first use this function)
125874_0_15748.cpp:105: error: (Each undeclared identifier is reported only once for each function it appears in.)
125874_0_15748.cpp: In function `int main()':
125874_0_15748.cpp:200: error: `plus' undeclared (first use this function)