foo.cc: In function 'int main()':
foo.cc:7:18: error: 'gcd' was not declared in this scope
    7 |  printf("%d",a*b/gcd(a,b));
      |                  ^~~
foo.cc:6:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    6 |  scanf("%d %d",&a,&b);
      |  ~~~~~^~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务