View Compilation Error

0_0_30042072_16717.c:3:12: error: expected ';', ',' or ')' before '&' token
 int in(int &a,int &b){return scanf("%d%d",&a,&b);}
            ^
0_0_30042072_16717.c:8:4: error: variably modified 'ans' at file scope
 db ans[N];
    ^
0_0_30042072_16717.c: In function 'main':
0_0_30042072_16717.c:13:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for(int i=3;i<=2e5;i++)ans[i]=ans[i-2]*i/(i+1);
     ^
0_0_30042072_16717.c:13:5: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code