generate a birthday date randomly in c

int nombreAlea(int min, int max){
    return (rand()%(max-min+1) + min);
}

int main () {
    srand(time(0));
    int annee=nombreAlea(1940,2003),mois=nombreAlea(1,12),jour;
    /// le traitement de la date
    if((mois==1)||(mois==3)||(mois==5)||(mois==7)||(mois==8)||(mois==10)||(mois==12)) jour = nombreAlea(1,31);
    if((mois==4)||(mois==6)||(mois==9)||(mois==11)) jour = nombreAlea(1,30);
    if(mois==2)
    {if (annee % 4 == 0 )
            jour = nombreAlea(1,28);
        else
            jour = nombreAlea(1,29);
    }
    
    /// the format of the date is  jj/mm/aaaa
    signed char Date[20];
    signed char jour_c[3],mois_c[3],annee_c[6];
    itoa(jour,jour_c,10);
    itoa(mois,mois_c,10);
    itoa(annee,annee_c,10);
    Date[0]=jour_c[0];
    Date[1]=jour_c[1];Date[2]='/';
    Date[3]=mois_c[0];Date[4]=mois_c[1];Date[5]='/';
    Date[6]=annee_c[0];Date[7]=annee_c[1];Date[8]=annee_c[2];Date[9]=annee_c[3];Date[10]='\0';
    printf("%s",Date); 
    
    return 0 ;
}

i want to generate a birthday day randomly , but the problem is that sometimes i get the half of the date , and smetimes i get only 2 caracters , and i don't understand where s the problem , any help !