View Compilation Error

0_0_27478482_21138.cpp:4:5: error: stray '\' in program
     double a,b\;
     ^
0_0_27478482_21138.cpp: In function 'int main()':
0_0_27478482_21138.cpp:7:14: error: 'abs' was not declared in this scope
       b=abs(a);
              ^