In this example, you are using the selection structure because a decision whether a number is even or odd must be made. This decision can be made with the help of the built-in function MOD. This function returns the remainder of the NUMBER divided by 2. If a number is divisible by 2 (in other words, there is no remainder), then it is an even number. Otherwise, a number is an odd number.
Assume that the number is equal to 16. The value returned by the MOD(16,2) is equal to 0. So the selection structure displays a message 'THIS NUMBER IS EVEN'. Next , assume that the number is equal to 7. The value returned by MOD(7,2) is equal to 1. So the select structure displays a message 'THIS NUMBER IS ODD'.
This structure is a combination of two structures: iteration and selection. The iteration structure repeats its steps for each number in the list. The selection structure makes a decision based on a particular number.
Assume that you have three numbers in your list: 10, 25, and 36. You start with the first number, 10. There are two more numbers left in the list. Next, the control of the flow is passed to the selection structure. Because the current number equals 10, the value returned by the MOD function is equal to 0. As a result, the message 'THIS NUMBER IS EVEN' is displayed. Then the control of the flow passed back to the iteration structure, and you are ready to move to the next number. The next number is equal to 25, and the value retuned by the MOD function is equal to 1. As a result, the message 'THIS NUMBER IS ODD' is displayed. Next, the control of the flow is passed back to the iteration structure to process the last number in the list, 36. This is an even number, so the selection structure displays the message 'THIS NUMBER IS EVEN'.