View Compilation Error

0_0_28383994_25871.cpp: In function 'int main()':
0_0_28383994_25871.cpp:12:32: error: unable to find character literal operator 'operator""a' with 'char' argument
   else if(a[0]=='+'||a[len-1]=='+'a[0]=='*'||a[len-1]=='*')
                                ^