[C] Maudites structures.....

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

main()
 {
  struct db_integers{  // Octets
    char *boolean;                // 1 bit
    char *octet;                     // 1
 };

 struct db_integers *mysql_integers;  // pointeur
 mysql_integers=malloc(sizeof(struct db_integers));

 mysql_integers->boolean="BOOL";
 mysql_integers->octet="TINYINT";

 printf("%s\n",mysql_integers->boolean);
 printf("%s\n",mysql_integers->octet);
}

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

main()
{
 struct db_integers{  // Octets
     char *boolean;                // 1 bit
     char *octet;                     // 1
 };

 typedef struct db_integers integers;
 integers *mysql_integers;  //pointeur
 mysql_integers=malloc(sizeof(integers));
 
 mysql_integers->boolean="BOOL";
 mysql_integers->octet="TINYINT";

 printf("%s\n",mysql_integers->boolean);
 printf("%s\n",mysql_integers->octet);
}

champollion.c:11: error: conflicting types for `mysql_integers'
champollion.c:10: error: previous declaration of `mysql_integers'
champollion.c:11: attention : data definition has no type or storage class
champollion.c:13: error: erreur de syntaxe before '->' token

//a.c
#include <stdio.h>
#include <stdlib.h>
main()
{
test();
}

//b.c
test()
{
  struct db_integers
   {  // Octets
         char *boolean;                // 1 bit
         char *octet;                     // 1
   };
typedef struct db_integers integers;

integers *mysql_integers;
mysql_integers=malloc(sizeof(integers));

mysql_integers->boolean="BOOL";
mysql_integers->octet="TINYINT";

printf("%s\n",mysql_integers->boolean);
printf("%s\n",mysql_integers->octet);
}

gcc -c a.c
gcc -c b.c
gcc -o ab a.o b.o

typedef struct db_integers integers;
integers mysql_integers;
mysql_integers.boolean="BOOL";

struct machin{
        int a;
        double b;
};

struct machin var_machin;
var_machin.a=3;

int main()
{
}

struct machin{
        int a;
        double b;
};

struct machin var_machin;

void initialize_var_machin(void)
{
            var_machin.a=3;
}

int main()
{
	initialize_var_machin();
}

essai.c:8: error: erreur de syntaxe before '.' token

#ifndef MYSTRUCT
#define MYSTUCT

typedef struct machin * pstruct;

pstruct new_struct();
void set_a(pstruct s,int val);
void set_b(pstruct s,double vall);
void del_struct(pstruct s);

#endif

#include "mystruct.h"

struct machin{
int a; 
double b;
};
//....

#include <stdio.h>
struct machin{
       int a;
};
struct machin var_machin;
main()
{
var_machin.a=3;
printf("%d\n",var_machin.a);
}

#include <stdio.h>
struct machin{
       int a;
       char nom[10];
};
/*affectation globale */
struct machin var_machin ={ 3, "kilian" };

main()
{
 printf("%d\n",var_machin.a);
 printf("%s\n",var_machin.nom);
}