foo.c: In function ‘main’:
foo.c:7:16: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    7 |         printf("");
      |                ^~
foo.c:9:16: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    9 |         printf("");
      |                ^~
foo.c:11:19: error: ‘std’ undeclared (first use in this function)
   11 |         c=(a1*a2)/std::__gcd(a1,a2);
      |                   ^~~
foo.c:11:19: note: each undeclared identifier is reported only once for each function it appears in
foo.c:11:22: error: expected ‘;’ before ‘:’ token
   11 |         c=(a1*a2)/std::__gcd(a1,a2);
      |                      ^
      |                      ;
foo.c:17:14: error: expected ‘;’ before ‘:’ token
   17 |         g=std::__gcd(f,c);
      |              ^
      |              ;
foo.c:6:25: warning: unused variable ‘sum’ [-Wunused-variable]
    6 |         int b1,a1,b2,a2,sum,c,d,e,f,g;
      |                         ^~~