Tutorial/Accumulate/Count-old

You may find the page on accumulating variables useful:

[http://progzoo.net/tut.cgi/java/ht70Tech/100Acc.xml Using an accumulator.]

How many countries in Asia?

In this example we use an accumulator to count the countries in Africa.

Notice that acc shows up three times:

The accumulator acc is set to zero at the start.

• Every time we encounter Africa we increment acc.
• After the loop has completed acc contains the value

we want - so we print it.

Change the program so that it counts the countries of Asia. Do NOT include the countries of Southeast Asia.

increment

Increment is a fancy word for increase - usually we mean add 1. The code acc++ adds 1 to the variable acc.
Take guess at what acc-- would do.

Getting 41 countries?

Using the test line.contains("Asia") will not work as the countries of SOutheast Asia include the substring "Asia". Instead we should test the region varaible using region.equals

The accumulating variable is a very common trick in programming. The accumulator builds up the values - so that it is "right-so-far". For example in this program acc always holds the number of countries in Africa in the lines that have been read so far.

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import java.io.BufferedReader; import java.io.FileReader; public class Cia{ public static void main(String[] argv) throws Exception{ BufferedReader fh = new BufferedReader(new FileReader("cia.txt")); String line; int acc = 0; while ((line=fh.readLine())!=null){ String f[] = line.split("\t"); String name = f[0]; String region = f[1]; int area = Integer.parseInt(f[2]); int pop = Integer.parseInt(f[3]); long gdp = Long.parseLong(f[4]); if (line.contains("Africa")) { acc++; } } System.out.println(acc); } }

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test text

 

 

 

 

How many big countries?

Count the number of countries with an area of more than 1500000.

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import java.io.BufferedReader; import java.io.FileReader; public class Cia{ }

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test text

 

 

 

 

Numbering countries.

Produce a numbered list of countries:

1 Afghanistan
2 Albania
3 Algeria
...
262 Zimbabwe

Use three character spaces for the number and put a single space after it.

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import java.io.BufferedReader; import java.io.FileReader; public class Cia{ }

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test text

 

 

 

 

Country number 42.

Print the name of country number 42

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import java.io.BufferedReader; import java.io.FileReader; public class Cia{ }

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test text