\queu\main.c|10|error: two or more data types in declaration of `add'

#include <stdio.h>
#include <stdlib.h>

typedef struct chain
{
    int elem;
    struct chain *next;
} chain;
chain *first=NULL, *last=NULL;

void add(int elem);
void get();

int main()
{
    int elem;
    char op;
    do
    {
        printf("Input option (a-add, g-get, any key-quit): ");
        fflush(stdin);
        scanf("%c",&op);

        if(op=='a')
        {
            scanf("%d",&elem);
            add(elem);
        }
        if(op=='g')
            get();


    }while((op=='a') ||(op=='g'));
    return 0;
}

void get()
{

    if (first!=NULL)
    {
        chain *p=NULL;
        printf("Element: ");
        printf("%d\n",first->elem);
        p=first;
        if ((first=first->next)==NULL)
            last=NULL;
        free(p);
        p=NULL;
    }
    else
        printf("No-no-no David Blain!!! O_o\n");
}

void add(int elem)
{
    chain *p=NULL;
    p=malloc(sizeof(chain));
    p->elem=elem;
    p->next=NULL;
    if (first==NULL)
        first=p;
    else
        last->next=p;
    last=p;
}