Error: Array type has incomplete element type and binary operand error

Error: Array type has incomplete element type and binary operand error

I am trying to make a multi-program database in C.
Here is the code:
#include<stdio.h>
#include<stdlib.h>
#include "function.c"
int main()
{
info();
example();
printf("\n\n\n");
char name[1][10], id[1][10], grade[1][1];
char choice;
int x=0;
int sal[1];
FILE *fp;
printf("Would you like to continue? Y/N: ");
scanf("%c",&choice);
fflush(stdin);
if(choice == 'Y' || choice == 'y')
{
system("cls");
fp = fopen("database.txt","w");
if(fp == NULL)
{
printf("File does not exist!");
return 0;
}
else
{
while(x<=1)
{
printf("Enter Employee name no.%d: ",(x+1));
scanf("%s",name[x]);
fprintf(fp, "Employee Name: %s\n",name);
printf("Enter Employee ID: ");
scanf("%s",id[x]);
fprintf(fp, "Employee ID: %s\n",id);
printf("Enter Employee Grade Level (A-E): ");
scanf("%s",grade[x]);
fprintf(fp, "Employee Grade Level: %s\n",grade);
printf("Enter Employee's Basic Salary: ");
scanf("%d",&sal[x]);
fprintf(fp, "Employee's Basic Salary: %d\n\n\n",sal);
printf("Employee's bonus: %d\n",bonus(grade[x],sal[x]));
printf("Employee's allowance: %d\n",allowance(grade[x], sal[x]));
printf("\n");
}
}
fclose(fp);
}
else
{
return 0;
}
return 0;
}
function.c :
#include<stdio.h>
#include "function.h"
int bonus(char *grade[1][], int *sal[])
{
int bonus;
int *b;
int x;
b = &bonus;
for(x=0;x<=1;x++)
{
switch(*grade[x])
{
case 'A':
bonus = (1/4) * *sal[x];
break;
case 'B':
bonus = (1/5) * *sal[x];
break;
case 'C':
bonus = (15/100) * *sal[x];
break;
case 'D':
bonus = (1/10) * *sal[x];
break;
case 'E':
bonus = (5/100) * *sal[x];
break;
default:
printf("Invalid Choice!!");
break;
}
return bonus;
}
}
int allowance(char *grade[1][], int *sal[])
{
int all;
int *a;
int x;
a = &all;
for(x=0;x<=1;x++)
{
switch(*grade[x])
{
case 'A':
all = (3/10) * *sal[x];
break;
case 'B':
all = (6/25) * *sal[x];
break;
case 'C':
all = (9/50) * *sal[x];
break;
case 'D':
all = (3/25) * *sal[x];
break;
case 'E':
all = (3/50) * *sal[x];
break;
default:
printf("Invalid Choice!!");
break;
}
return all;
}
}
When I try to run the program, I get:
2 0 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c In file included from C:\Users\nithin\Desktop\Online
Courses\C Programming\Final Project\function.c 4 17
C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.h [Error] array type has incomplete element type 5 21
C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.h [Error] array type has incomplete element type 4 17
C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] array type has incomplete element type
C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c In function 'bonus': 18 19
C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 21 19 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 24 22 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 27 20 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 30 21 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c At top level: 41 21 C:\Users\nithin\Desktop\Online
Courses\C Programming\Final Project\function.c [Error] array type has
incomplete element type C:\Users\nithin\Desktop\Online Courses\C
Programming\Final Project\function.c In function 'allowance': 54 17
C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 57 17 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 60 17 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 63 17 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *') 66 17 C:\Users\nithin\Desktop\Online Courses\C Programming\Final
Project\function.c [Error] invalid operands to binary * (have 'int' and
'int *')
I do not know what the problem is (I'm a beginner in C programming).
My first question: What does array type has incomplete element type mean?
Next question: Why am I still getting the invalid operands to binary *
error?
Any help would be appreciated.