159.234 OBJECT-ORIENTED PROGRAMMING TUTORIAL 2

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159.234 OBJECT-ORIENTED PROGRAMMING

Tutorial 2

Task 1: Review the content of Lecture 05 _ Java Control Structures, answer the following questions:

1.   What is the main difference between a while loop and a do..while loop?

Both types of loops repeat a block of statements until some condition becomes false. The main difference is that in a while loop, the condition is tested at the beginning of the loop, and in a do…while loop, the condition is tested at the end of the loop. It is possible that the body of a while loop might not be executed at all. However, the body of a do…while loop is executed at    least once since the condition for ending the loop is not tested until the body of the loop has been executed.

2.   Write a for loop that will print out all the multiples of 3 from 3 to 36, that is: 3 6 9 12 15 18 21 24 27 30 33 36.

Here are two possible answers. Assume that N has been declared to be a variable of type int:

for ( N = 3;  N <= 36;  N = N + 3 ) {

System.out.println( N );

}

or

if ( N % 3 == 0 )

System.out.println( N );

}

3.   Suppose that numbers is an array of type int[]. Write a code segment that will count and output the number of times that the number 42 occurs in the array.

Use a for loop to go through the array and test each array element. If the value is 42, add 1 to a counter:

int count42;  // The number of 42s in the array

count42 = 0;

int i;  // loop control variable

for ( i = 0; i < numbers.length; i++ ) {

if ( numbers[i] == 42 ) {

count42++;

}

}

System.out.println("There were " + count42 + " 42s in the array.")