Main.cc: In function ‘int main()’:
Main.cc:6:15: warning: format ‘%lld’ expects argument of type ‘long long int*’, but argument 2 has type ‘int*’ [-Wformat=]
    6 |     scanf("%lld %lld",&a,&b);
      |            ~~~^       ~~
      |               |       |
      |               |       int*
      |               long long int*
      |            %d
Main.cc:6:20: warning: format ‘%lld’ expects argument of type ‘long long int*’, but argument 3 has type ‘int*’ [-Wformat=]
    6 |     scanf("%lld %lld",&a,&b);
      |                 ~~~^     ~~
      |                    |     |
      |                    |     int*
      |                    long long int*
      |                 %d
Main.cc:4:17: warning: unused variable ‘gcd’ [-Wunused-variable]
    4 |     int a,b,s,t,gcd;
      |                 ^~~
Main.cc: In function ‘void exgcd(long long int, long long int, int*, int*)’:
Main.cc:17:16: error: return-statement with a value, in function returning ‘void’ [-fpermissive]
   17 |         return a;
      |                ^
Main.cc:19:18: error: void value not ignored as it ought to be
   19 |     int ret=exgcd(b,a%b,x,y);
      |             ~~~~~^~~~~~~~~~~
Main.cc:23:12: error: return-statement with a value, in function returning ‘void’ [-fpermissive]
   23 |     return ret;
      |            ^~~
Main.cc: In function ‘int main()’:
Main.cc:6:10: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
    6 |     scanf("%lld %lld",&a,&b);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~