Control Statements in SQL

8 Key excerpts on "Control Statements in SQL"

• 

  eBook - ePub

  Introduction to Programming

  Learn to program in Java with data structures, algorithms, and logic

  • Nick Samoylov(Author)
  • 2018(Publication Date)
  • Packt Publishing

    (Publisher)

  Control Flow Statements

  This chapter describes one particular kind of Java statement

  , called control statements, which allow the building of a program flow according to the logic of the implemented algorithm, which includes selection statements, iteration statements, branching statements, and exception handling statements.

  In this chapter, we will cover the following topics:

  • What is a control flow?
  • Selection statements: if, if....else, switch...case
  • Iteration statements: for, while, do...while
  • Branching statements: break, continue, return
  • Exception handling statements: try...catch...finally, throw, assert
  • Exercise – Infinite loop

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  What is a control flow?

  A Java program is a sequence of statements that can be executed and produce some data or/and initiate some actions. To make the program more generic, some statements are executed conditionally, based on the result of an expression

  evaluation. Such statements are called control flow statements because, in computer science, control flow (or flow of control) is the order in which individual statements are executed or evaluated.

  By convention, they are divided into four groups: selection statements, iteration statements, branching statements, and exception handling statements. In the following sections, we will use the term block, which means a sequence of statements enclosed in braces. Here is an example: { x = 42; y = method(7, x); System.out.println("Example"); } A block can also include control statements – a doll inside a doll, inside a doll, and so on.

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  Selection statements

  The control flow statements of the selection statements group are based on an expression evaluation. For example, here is one possible format: if(expression) do something. Or, another possible format: if(expression) {do something} else {do something else}.

  The expression may return a boolean value (as in the previous examples) or a specific value that can be compared with a constant. In the latter case, the selection statement has the format of a switch statement, which executes the statement or block that is associated with a particular constant value.

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  eBook - ePub

  C Programming

  Learn to Code

  • Sisir Kumar Jena(Author)
  • 2021(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  Selection Control Structure: This is also known as decision control structure, and it ensures the computer makes decisions about which statement is to be executed next. Figure 8.2b shows the flow of execution. After executing Statement 2, the compiler arrives at Statement 3 which is a condition, and if the condition is satisfied (is true) then the compiler executes Statements 4, 5, and 6, otherwise it executes 7, 8, and 9.
• Loop Control Structure: This helps the computer to execute group/single statements repeatedly until a condition is satisfied. Figure 8.2c shows the flow of execution. The compiler executes Statements 4 through 6 repeatedly until the condition becomes true, and the moment it is false, it starts its execution from Statement 7 onwards.
Figure 8.2 Categories of control statements.
All programs discussed so far come under the sequence control structure. In this chapter, we will introduce several programs that will reflect the properties of the selection and loop control structure. After completing this chapter, the student will know the following:
• What different control structures are available in the C language.
• The syntax of different control structures.
• Be able to differentiate between sequence and selection control structure.
• Write code for more realistic problems.
• What a compound statement is.
The C language provides several keywords for control structure declaration. We classify all those keywords according to our control structure category. Figure 8.3 shows a detailed classification of all control statements and introduces several new keywords. We divide the selection control statements into two groups, because some selection statements do not require conditions; we can break the flow of execution arbitrarily.
Figure 8.3 Classification of control structure.
In the next section we will discuss all control statements, their syntaxes, flowcharts, and some example programs that show their properties and execution procedure.

8.2 Selection with if Statements

Suppose we are executing a set of instructions, and we want some instruction to execute only when a specific condition is satisfied. With the help of an if selection control statement, we can achieve this. The syntax of if, with and without a compound statement, is shown in Figure 8.4