/in/foo.c:3:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:3:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c: In function 'main':
/in/foo.c:7:5: error: 'cin' undeclared (first use in this function)
     cin>>l>>m;
     ^~~
/in/foo.c:7:5: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:8:5: error: variable-sized object may not be initialized
     int a,b,c[l+1]={0};//搞数值和线段
     ^~~
/in/foo.c:8:21: warning: excess elements in array initializer
     int a,b,c[l+1]={0};//搞数值和线段
                     ^
/in/foo.c:8:21: note: (near initialization for 'c')
/in/foo.c:18:5: error: 'cout' undeclared (first use in this function)
     cout<<s;//最后输出
     ^~~~