/in/foo.cc: In function 'int mian()':
/in/foo.cc:6:14: warning: 'x1' is used uninitialized [-Wuninitialized]
    6 |         a=abs(x1-x2);
      |           ~~~^~~~~~~
/in/foo.cc:5:16: note: 'x1' was declared here
    5 |         double x1,x2,y1,y2,a,b,pfh;
      |                ^~
/in/foo.cc:6:14: warning: 'x2' is used uninitialized [-Wuninitialized]
    6 |         a=abs(x1-x2);
      |           ~~~^~~~~~~
/in/foo.cc:5:19: note: 'x2' was declared here
    5 |         double x1,x2,y1,y2,a,b,pfh;
      |                   ^~
/in/foo.cc:7:14: warning: 'y1' is used uninitialized [-Wuninitialized]
    7 |         b=abs(y1-y2);
      |           ~~~^~~~~~~
/in/foo.cc:5:22: note: 'y1' was declared here
    5 |         double x1,x2,y1,y2,a,b,pfh;
      |                      ^~
/in/foo.cc:7:14: warning: 'y2' is used uninitialized [-Wuninitialized]
    7 |         b=abs(y1-y2);
      |           ~~~^~~~~~~
/in/foo.cc:5:25: note: 'y2' was declared here
    5 |         double x1,x2,y1,y2,a,b,pfh;
      |                         ^~
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/Scrt1.o: in function `_start':
(.text+0x17): undefined reference to `main'
collect2: error: ld returned 1 exit status