C program gets an invalid conversion in a function - c

Question

I have few error commented after this text, i don't get what the compiler is trying to say me, the last function is in to do list i hope that's not the problem, the problem is i want to ask the user for 2 chars after that its send to a function who will compare the strings as a password and a login if the strings are the same, the program continues.
\\initializing argument 1 of int consultar(char, char)\\
\\invalid conversion from char*' to `char' \\
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
void introducir_datos (struct agenda cliente[30]);
void mostrar_datos(struct agenda cliente[30]);
char consultar(char login,char password);
struct agenda{
char nombre[10];
char apellido[10];
int edad;
char direccion[20];
int codigo_postal;
};
int main(void)
{
struct agenda cliente[30];
int menu;
char con[3],login[8], password[8];
puts("\n=== Hola bienvenido a nuestra agenda en C ===\n");
puts("Login:");
gets(login);
puts("Password:");
gets(password);
**consultar(login, password);**
while ( menu != 3){
puts("\nQue quieres hacer?\n");
puts("[1]Insertar datos\n[2]Mostrar datos\n[3]Salir del programa\n");
scanf("%d", &menu);
switch(menu){
case 1:
introducir_datos(cliente);
break;
case 2:
mostrar_datos(cliente);
break;
default:
system("cls");
puts("~~~ Opcion incorrecta ~~~");
}
}
}
void introducir_datos (struct agenda cliente[30]){
int x = 0;
puts("\n=== Bienvenido a la introduccion de datos ===\n");
fflush(stdin);
system("pause");
system("cls");
puts("\nDime el nombre:\n");
fflush(stdin);
gets(cliente[x].nombre);
puts("\nDime el apellido:\n");
fflush(stdin);
gets(cliente[x].apellido);
puts("\nDime la edad:\n");
fflush(stdin);
scanf("%d",&cliente[x].edad);
puts("\nDime la direccion:\n");
fflush(stdin);
gets(cliente[x].direccion);
puts("\nDime el codigo postal:\n");
fflush(stdin);
scanf("%d",&cliente[x].codigo_postal);
x++;
}
void mostrar_datos(struct agenda cliente[30]){
for(int i=0;i<20;i++){
int x = 0;
printf("El nombre: %s \nEl apellido: %s\nEl edad: %d\nEl direccion: %s\nEl codigo postal: %d\n", cliente[x].nombre,cliente[x].apellido,cliente[x].edad,cliente[x].direccion,cliente[x].codigo_postal);
}
}
int consultar(char login, char password){
}

Answer 1

You need to change the consultar function (definition and implementation):
int consultar(char login, char password)
to:
int consultar(char *login, char *password)
If you use (char login, char password), it's looking for a single character. Since, by calling it with consultar(login, password);, you're using pointers to char arrays (simplified explaination), you're getting the error.
EDIT As pointed out by user "Namfuak", you should decide whether the function returns a char or an int, and have both definition and implementation be consistent.