/in/foo.c:2:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c:5:5: error: variably modified 'a' at file scope
 int a[maxn1][maxn2];//卡塔兰数：每行是一个卡特兰数
     ^
/in/foo.c:5:5: error: variably modified 'a' at file scope
/in/foo.c:6:5: error: variably modified 'b' at file scope
 int b[maxn1];//卡特兰数的长度
     ^