Unit 5

“Same Song, Second Verse”Programming Loops

Introduction toC Programming

Review of Unit 4

Unit 5: Review of Past Material

Review of Past ConceptsRelational, Equality, and Logical OperatorsSyntax of the Compound StatementSyntax of the if statementSyntax of the if-else structureThe switch statement

Data type of the selectorCase label syntax and data typeDefault label

Short-Circuit EvaluationIncrement/Decrement Operators

Unit 5: Advanced Operators

Short-Circuit EvaluationLogical "and" operator (&&)

The first operand is evaluatedThe second operand will not be evaluated if the first

is false

(4 > 7) && (x++ == 2)

Logical "or" operator (||)The first operand is evaluatedThe second operand will not be evaluated if the first

is true (4 > 3) && (x++ == 2)

Beware of "side-effects" not occurring as expected

Increment and Decrement OperatorsThe C increment operator is the "++"

operatorThe operator adds one to the variableint x = 4;

x = x + 1; /* Add one, x now is 5 */

++x; /* Same as above, x now is 6 */

To subtract one, use the decrement "--" operatorThe operator subtracts one from the variableint x = 4;

--x; /* Subtract one, x now is 3 */

Increment and Decrement OperatorsCan be combined into a larger expression

Prefix: the "++" or "--" comes before the variableThe variable is changed firstThe changed value is used in further calculations

int x = 4, y = 0;

y = ++x; /* x is 5, y is 5 */Postfix: the "++" or "--" comes after the

variableThe variable is changed lastThe value before change is used in further

calculations

int x = 4, y = 0;

y = x++; /* x is 5, but y is 4 */

Loop Structures

Unit 5: Loops

Basics of LoopsProgramming loops are iterative code structures

A set of instructions is repeated a number of timesLoops are controlled by a condition, or loop testA loop is preceded by an initialization

Sets up the loop condition for initial executionA loop contains an increment

Determines whether the loop continues or stops

Loops without a loop test repeat indefinitelyUseful for control systems or systems that "run

continuously"

Loop Structures - The "while" LoopLoop test is done first, at "top" of loopMay or may not execute once or more

int count;

count = 0; /* Initialization action */

while (count < 5) { /* Loop test (condition) */

/* Loop body - action to repeat */

++count; /* Loop increment */

}

Loop Structures - The "do-while" Loop

Loop test is done last, at "bottom" of loopAlways executes at least once

int count;

count = 0; /* Initialization action */

do {

/* Loop body - action to repeat */

++count; /* Loop increment */

} while (count < 5); /* Loop test (condition) */

Loop Structures - The "for" LoopThe "for" loop

Contains initialization, loop test, and increment all in one place

int count;

for (count = 0; count < 5; ++count) {

/* Loop body - action to repeat */

}

Different Loops for Different PurposesCounter-controlled loop

Loops a specific number of times as a counter increments

Conditional loopLoops until a specific condition becomes true

Sentinel-controlled loopProcesses data until a special value signals

the end of data

Modifying Loop ExecutionThe "break" statement break;

This is an immediate exit from a loopOnly used under unusual circumstances

The "continue" statement continue;Used to stop the current loop iterationBegins a new loop execution immediately

Principles of Structured Code

Unit 5: Structured Code

Structured CodeDesign principle for code

Entry at top of sectionExit at bottom of section

"Never" use the "goto" statementVery rare circumstances need "break" or

"continue" in loopAvoid "spaghetti code" - tangled, poorly

written code

Newton's Method

Unit 5: Loops

Newton's Method for Finding RootsNewton's Method is an iterative methodFinds Roots (solutions) of a polynomial equation

Example codeFind root of f(x) = 3x^3 - 5x^2 + 2x +3There is a real root at x = -0.538962

Newton's Method starts with a "guess" (e.g. use -4)

Calculates iteratively better estimates of root using:X = oldX - f(oldX) / f '(oldX) where f ' is the

derivativeCompares oldX with new X estimate

When difference is very small, the estimates have "converged"