solde is private. You can't use it outside of class for read and write.
Other is public, i.e. ok.
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Client c1, c2;
cout<<"Name de c1:"<<c1.name; //ok
cout<<"Solde de c1:"<<c1.solde; //no
cout<<"Solde de c1:"<<c1.getSolde(); ok
c2.solde=0; //no
c2.putSolde(12359.142); ok