Intro to C Chapter 4: Loops

While loops

A while loop is a program construct that repeatedly executes a list of sub-statements (known as the loop body) while the loop's expression evaluates to true. Each execution of the loop body is called an iteration. Once entering the loop body, execution continues to the body's end, even if the expression would become false midway through.

Infinite loop

An infinite loop is a loop that never stops iterating. A common error is to accidentally create an infinite loop, often by forgetting to update a variable in the body, or by creating a loop expression whose evaluation to false isn't always reachable.

Break statement

A break statement in a loop causes an immediate exit of the loop. A break statement can sometimes yield a loop that is easier to understand.

Continue statement

A continue statement in a loop causes an immediate jump to the loop condition check. A continue statement can sometimes improve the readability of a loop

increment and decrement operators

Increase/decrease the value of a variable by a particular amount. Addition: x += 1 will accomplish x = x + 1. Subtraction: x -= 2 will accomplish x = x - 2. Multiplication: x *= 5 will accomplish x = x * 5. To increment or decrement by one, do: x++ x---

Sentinel value

A sentinel value is a special value indicating the end of a list, such as a list of positive integers ending with 0, as in 10 1 6 3 0.

Variable name scope

A declared name is only valid within a region of code known as the name's scope. Ex: A variable userNum declared in main() is only valid within main(), from the declaration to main()'s end. Most of this material declares variables at the top of main() (and if the reader has studied functions, at the top of other functions). However, a variable may be declared within other blocks too. A block is a brace-enclosed {...} sequence of statements, such as found with an if-else, for loop, or while loop. A variable name's scope extends from the declaration to the closing brace }.

For Loops

A loop commonly must iterate a specific number of times, such as 10 times. Though achievable with a while loop, that situation is so common that a special kind of loop exists. A for loop is a loop with three parts at the top: a loop variable initialization, a loop expression, and a loop variable update. A for loop describes iterating a specific number of times more naturally than a while loop.

Loops

A loop is a program construct that repeatedly executes the loop's statements (known as the loop body) while the loop's expression is true; when false, execution proceeds past the loop. Each time through a loop's statements is called an iteration.

Nested Loops

A nested loop is a loop that appears in the body of another loop. The nested loops are commonly referred to as the inner loop and outer loop. Nested loops have various uses. One use is to generate all combinations of some items.

Enumerations

Some variables only need store a small set of named values. For example, a variable representing a traffic light need only store values named GREEN, YELLOW, or RED. An enumeration type declares a name for a new type and possible values for that type.