Main.c: In function 'main':
Main.c:7:5: error: 'a' undeclared (first use in this function)
    7 |     a=m+n;
      |     ^
Main.c:7:5: note: each undeclared identifier is reported only once for each function it appears in
Main.c:8:5: error: 'b' undeclared (first use in this function)
    8 |     b=o+p;
      |     ^