The difference between ‘stop’ followed by infinitives and gerunds

Look at the following sentences.
1 I stopped to buy newspapers from the shop. [‘stop’ followed by infinitive ‘to buy’]
2 I stopped buying newspapers from the shop.[‘stop’ followed by gerund ‘buying’]

The above two sentences are different in meanings.

In sentence 1, it means ‘ I stopped ( my car) and went into the shop to buy newspapers.’ whereas sentence 2 carries the meaning of ‘I did not want to buy newspapers from the shop anymore and so I stopped my action of doing so.’

See whether you can explain the meanings of the following pairs of sentences.
1 a) John stopped to smoke.
b) John stopped smoking.

2 a) She stopped to exercise in the garden.
b) She stopped exercising in the garden.

3 a) I stopped to talk to him.
b) I stopped talking to him.