several Compile Errors when using GCC

I am trying to upload a solution to an OJ ,the judge uses GCC I have received the following errors and having no idea about them.

error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘{’ token
void insert(int in){
^

In function ‘main’:
error: ‘struct mymultiset_int’ has no member named ‘insert’
x.insert(t);
^

error: ‘struct mymultiset_int’ has no member named ‘getmax’
printf("%d\n",x.getmax());
^
error: ‘struct mymultiset_int’ has no member named ‘_delete’
x._delete(0);
^

My code looks like this:

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
int t;
#define swap(a,b) t=b,b=a,a=t
/*
when using swap, I use format like swap(x,y); or swap(x,y),
*/

struct mymultiset_int{
    int e[100000],end;
    void insert(int in){...}
    int getmax(){ return e[0]; }
    void _delete(int i){...}
}x;
int main(){
    x.end=0;memset(x.e,0,sizeof(x.e));
    int N,t;scanf("%d",&N);
    char i[2];
    while (N--){
        scanf("%s",i);
        if (i[0]=='A'){
            scanf("%d",&t);
            x.insert(t);
        }
        else{
            printf("%d\n",x.getmax());
            x._delete(0);
        }
    }
}