View Compilation Error

0_0_6873412_26173.cpp: In function `double kfun(char*, int&)':
0_0_6873412_26173.cpp:27: error: `abs' undeclared (first use this function)
0_0_6873412_26173.cpp:27: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_6873412_26173.cpp:27: error: `flag' undeclared (first use this function)
0_0_6873412_26173.cpp: At global scope:
0_0_6873412_26173.cpp:36: error: `int flag' used prior to declaration