構造体のリスト構造の課題なんですがコンパイルエラーの理由がわかりません

前提・実現したいこと

構造体について勉強したばかりでして、多くの自分では理解不可能なコンパイルエラーが出てきてしまいます。
それぞれの対処法をどうか教えてください。

発生している問題・エラーメッセージ

report4-pro.c:6:29: warning: declaration of 'struct record' will not be visible
outside of this function [-Wvisibility]
void add(char *trans,struct record *topad);
^
report4-pro.c:7:25: warning: declaration of 'struct record' will not be visible
outside of this function [-Wvisibility]
void displaylist(struct record *topad);
^
report4-pro.c:16:6: error: conflicting types for 'add'
void add(char *trans,struct record *topad){
^
report4-pro.c:6:6: note: previous declaration is here
void add(char *trans,struct record *topad);
^
report4-pro.c:22:18: warning: comparison of array 'list->word' equal to a null
pointer is always false [-Wtautological-pointer-compare]
if(list->word=='\0'){
report4-pro.c:51:6: error: conflicting types for 'displaylist'
void displaylist(struct record *topad){
^
report4-pro.c:7:6: note: previous declaration is here
void displaylist(struct record *topad);
^
report4-pro.c:93:23: warning: incompatible pointer types passing
'struct record *' to parameter of type 'struct record *'
[-Wincompatible-pointer-types]
add(trans,topad);

report4-pro.c:6:37: note: passing argument to parameter 'topad' here
void add(char *trans,struct record *topad);
^
report4-pro.c:101:17: warning: incompatible pointer types passing
'struct record *' to parameter of type 'struct record *'
[-Wincompatible-pointer-types]
displaylist(topad);

report4-pro.c:7:33: note: passing argument to parameter 'topad' here
void displaylist(struct record *topad);

該当のソースコード

c
1#include<stdio.h>
2#include<stdlib.h>
3#include<ctype.h>
4#include<string.h>
5
6void add(char *trans,struct record *topad);
7void displaylist(struct record *topad);
8
9struct record{
10    char word[100];
11    struct record *next;
12    struct record *back;
13    int frequency;
14};
15
16void add(char *trans,struct record *topad){
17    struct record *list;
18    struct record *newstr;
19    list = topad;
20    list->frequency=1;
21    while(0==0){
22        if(list->word=='\0'){
23            strcpy(list->word,trans);
24            break;
25        }
26        if(strcasecmp(list->word,trans)<0) list = list->next;
27        if(strcasecmp(list->word,trans)==0){
28            list->frequency++;
29            break;
30        }
31        if(strcasecmp(list->word,trans)>0){
32            newstr = (struct record*)malloc(sizeof(struct record));
33            strcmp(newstr->word,trans);
34            list->back->next=newstr;
35            newstr->back=list->back;
36            list->back=newstr;
37            newstr->next=list;
38            break;
39        } 
40        if(list->next==NULL){
41            newstr = (struct record*)malloc(sizeof(struct record));
42            strcmp(newstr->word,trans);
43            list->next=newstr;
44            newstr->back=list;
45            newstr->next=NULL;
46            break;
47        }
48    }
49}
50
51void displaylist(struct record *topad){
52    struct record *list;
53    list=topad;
54    while(list!=NULL){
55        printf("word:%s frequency:%d",list->word,list->frequency);
56        list=list->next;
57    }
58}
59
60int main(int argc,char *argv[]){ 
61    struct record Topad;
62    struct record *topad;
63    topad=&Topad;
64    char buf[5120];
65    char key[100];
66    char trans[100];
67    int wordnum=0; 
68    int keynum=0; 
69    int firsti,letnum,t,p,i;
70    
71    printf("キーワードを入力してください\n");
72    scanf("%s",key);
73    FILE *fp;
74    fp=fopen(argv[1],"r");
75    while(fgets(buf,sizeof(buf),fp) != NULL){
76        printf("%s",buf); 
77        i=0;
78        p=0;
79        while(*(buf+i)!='\0'){ 
80            while(isalnum(*(buf+i))==0&&*(buf+i)!='\0'){  
81                i++;
82            }
83            firsti=i; 
84            if(*(buf+i) == '\0') break;   
85            while(isalnum(*(buf+i))!=0){   
86                    i++;
87            } 
88            wordnum++; 
89            letnum = i-firsti; 
90            for(t=0;t<letnum;t++){ 
91                *(trans+t)=*(buf+firsti+t);
92            }
93            add(trans,topad);
94            if(strcasecmp(key,trans)==0) keynum++; 
95            memset(trans, '\0', sizeof(trans));   
96            while(isalnum(*(buf+i))==0&&*(buf+i)!='\0'){
97                i++;
98            }
99        }
100    }
101    displaylist(topad);
102    printf("\n単語数=%d\nキーワード数=%d\n出現頻度=%f\n",wordnum,keynum,(float)keynum/(float)wordnum);
103    fclose(fp);
104    exit(0);
105}