I have a validation in 3 days and my projects does not work !!!! please help

[high_flyer]

Your error is an ODBC/SQL error - the sequence of operations you are doing on the query is not right.
You probably will get more help from SQL/ODBC related forums.

However on a C++ level one thing seems odd in your code:

convention *c =new convention(id_c, nom_entreprise,pourcentage_c, date_expiration) ;
            c->ajouter_convention(c);

convention *c =new convention(id_c, nom_entreprise,pourcentage_c, date_expiration) ;
            c->ajouter_convention(c);

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Why are you creating an instance of 'convention' only to give it to it self?
Do you know what 'this' is?