foo.cpp: In function 'void gauss(double**, double**)':
foo.cpp:21:15: warning: unused variable 'p' [-Wunused-variable]
     int i,j,s,p,q,r=0,id;
               ^
foo.cpp:21:17: warning: unused variable 'q' [-Wunused-variable]
     int i,j,s,p,q,r=0,id;
                 ^
foo.cpp: In function 'int main()':
foo.cpp:67:17: warning: unused variable 'q' [-Wunused-variable]
     int i,j,s,p,q,jx,jy,pre,nx,ny;
                 ^
foo.cpp:67:25: warning: unused variable 'pre' [-Wunused-variable]
     int i,j,s,p,q,jx,jy,pre,nx,ny;
                         ^~~
foo.cpp: In function 'void gauss(double**, double**)':
foo.cpp:34:9: warning: 'id' may be used uninitialized in this function [-Wmaybe-uninitialized]
         if(id!=r)
         ^~