Here are the sentences converted into reported speech:

1. Tom said (that) he wanted to buy a pocket calculator for his father.
2. She said (that) she had spent a summer in Canada.
3. She said (that) she was going to become a doctor.
4. Mr. Brown said (that) their trip had cost them two thousand dollars.
5. He told her (that) he couldn't find his hat anywhere in that room.
6. My father said to them (that) his secretary was going to finish that job.
7. They said (that) they couldn't meet us there either the next day or the day after.
8. My mother said (that) she thought it wouldn't rain the next day.
9. He said (that) John's car had been stolen.
10. They said (that) the river was rising early that year.
11. He said (that) he would expect her to come soon.
12. Our teacher said (that) World War II had broken out in 1939.
13. The students said (that) they would be sitting for their next exam the following Monday.
14. He said (that) he was going to finish that work.
15. He told her (that) she was his friend.
16. Johnny told his mother (that) he didn't know how to do that exercise.
17. My brother advised (that) she shouldn't eat so much sugar.
18. Paul said (that) he had to go home then.
19. "There is an accident," said the policeman. (This one remains unchanged as it's a statement.)