Flow Control Basic


(UCM ELP) #1

If else
An if statement can be followed by an optional else statement, which executes when the boolean expression is false. If the boolean expression evaluates to true , then the if block of code will be executed, otherwise else block of code will be executed.

A while loop statement repeatedly executes a target statement as long as a given condition is true.
Here, statement(s) may be a single statement or a block of statements. The condition may be any expression, and true is any non-zero value. The loop iterates while the condition is true.
When the condition becomes false, program control passes to the line immediately following the loop.

Here, key point of the while loop is that the loop might not ever run. When the condition is tested and the result is false, the loop body will be skipped and the first statement after the while loop will be executed.

do while
Unlike for and while loops, which test the loop condition at the top of the loop, the do…while loop checks its condition at the bottom of the loop.
A do…while loop is similar to a while loop, except that a do…while loop is guaranteed to execute at least one time.
Notice that the conditional expression appears at the end of the loop, so the statement(s) in the loop execute once before the condition is tested.
If the condition is true, the flow of control jumps back up to do, and the statement(s) in the loop execute again. This process repeats until the given condition becomes false.

for loop
A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
· The init step is executed first, and only once. This step allows you to declare and initialize any loop control variables. You are not required to put a statement here, as long as a semicolon appears.
· Next, the condition is evaluated. If it is true, the body of the loop is executed. If it is false, the body of the loop does not execute and flow of control jumps to the next statement just after the for loop.
· After the body of the for loop executes, the flow of control jumps back up to the increment statement. This statement can be left blank, as long as a semicolon appears after the condition.
· The condition is now evaluated again. If it is true, the loop executes and the process repeats itself (body of loop, then increment step, and then again condition). After the condition becomes false, the for loop terminates.

switch case
A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each case.