/in/foo.c: In function 'main':
/in/foo.c:11:11: warning: unused variable 'n' [-Wunused-variable]
  long int n=0;
           ^
/in/foo.c:10:13: warning: unused variable 'j' [-Wunused-variable]
  long int i,j,t,lor=0;
             ^
/in/foo.c:10:11: warning: unused variable 'i' [-Wunused-variable]
  long int i,j,t,lor=0;
           ^
/in/foo.c:9:21: warning: unused variable 'sum' [-Wunused-variable]
  long int a=0,b=0,N,sum=0;   //化为ax+b=0; 
                     ^~~
/in/foo.c:9:19: warning: unused variable 'N' [-Wunused-variable]
  long int a=0,b=0,N,sum=0;   //化为ax+b=0; 
                   ^
/in/foo.c:70:2: warning: 'x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%c=%.3lf",x,ans==0?abs(ans):ans);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~