16/27/2015 11:53 PM6/27/2015 11:53 PM6/27/2015 11:53 PMLogic Control Structures Arithmetic...

1104/18/2304/18/23 21:5921:59 Logic Control StructuresLogic Control Structures

Arithmetic ExpressionsArithmetic Expressions

Used to do arithmetic.Used to do arithmetic.

Operations consist of +, -, *, /, %, unary -+, Operations consist of +, -, *, /, %, unary -+, and function calls.and function calls.

Evaluate to real or integer values.Evaluate to real or integer values.


String ExpressionsString Expressions

Used to do string manipulation.Used to do string manipulation.Operations consist of string methods Operations consist of string methods ("object-oriented functions") and regular ("object-oriented functions") and regular functions.functions.Evaluate to string valuesEvaluate to string valuesString comparison is character-by-String comparison is character-by-character based on ASCII values (see character based on ASCII values (see appendix A in textbook) including the null appendix A in textbook) including the null terminator. So “10” < “2”.terminator. So “10” < “2”.


Relational ExpressionsRelational Expressions

Used to test the vales of two arithmetic Used to test the vales of two arithmetic expressions against each other, or to test expressions against each other, or to test the vales of two string expressions against the vales of two string expressions against each other.each other.

Operations consist of >, <, ==, !=, <=, >=.Operations consist of >, <, ==, !=, <=, >=.

Evaluate to boolean values (ie, true or Evaluate to boolean values (ie, true or false).false).


Boolean ExpressionsBoolean Expressions

AKA logical expressionsAKA logical expressions

Used to combine boolean values.Used to combine boolean values.

Operations consist of && (and), || (or), and Operations consist of && (and), || (or), and ! (not).! (not).

Evaluate to boolean values (ie, true or Evaluate to boolean values (ie, true or false).false).

See tables 4.3-4.5 in text book (page 170) See tables 4.3-4.5 in text book (page 170) for definitions of boolean operators.for definitions of boolean operators.


ConditionsConditions

Operations consist of arithmetic, string, Operations consist of arithmetic, string, relational, and boolean operators.relational, and boolean operators.Evaluate to boolean values (ie, true or Evaluate to boolean values (ie, true or false).false).See table 4.6 in text book (page 171) for See table 4.6 in text book (page 171) for precedence rules.precedence rules.Short-Circuit Evaluation: evaluation of Short-Circuit Evaluation: evaluation of expression stops when value of expression stops when value of expression is determined.expression is determined.


Basic Logic Control StructuresBasic Logic Control Structures

SequenceSequence

SelectionSelection

IterationIteration


SequenceSequence

Execution starts at the top of a block, and Execution starts at the top of a block, and execution proceeds line-by-line through execution proceeds line-by-line through the block; execution continues after the the block; execution continues after the sequence structure.sequence structure.

<block><block>


Selection (if)Selection (if)

A condition is evaluated, and if it is true, a A condition is evaluated, and if it is true, a block is executed; execution continues block is executed; execution continues after the selection structure.after the selection structure.

if (<condition>)if (<condition>)

<block><block>


Iteration (while)Iteration (while)

A condition is evaluated, and if it is true, a block A condition is evaluated, and if it is true, a block is executed; this is repeated until the condition is executed; this is repeated until the condition is false, then execution continues after the is false, then execution continues after the iteration structure. AKA indefinite iteration.iteration structure. AKA indefinite iteration.

while (<condition>)while (<condition>)

<block><block>


BlockBlock

A block consists of EITHER a single A block consists of EITHER a single statement terminated by a semi-colon OR statement terminated by a semi-colon OR a { followed by one or more statements a { followed by one or more statements each terminated by a semi-colon followed each terminated by a semi-colon followed by a } (technically, in either case, the by a } (technically, in either case, the statements are optional).statements are optional).


Nested Logic Control StructuresNested Logic Control Structures

A statement in a block may be another A statement in a block may be another logic control structure.logic control structure.These are the only three logic control These are the only three logic control structures (with nesting) needed to structures (with nesting) needed to develop any program.develop any program.Structured ProgrammingStructured Programming Programs that only use the above logic Programs that only use the above logic

control structures, ie, do not use the goto control structures, ie, do not use the goto statement.statement.


Additional Logic Control StructuresAdditional Logic Control Structures

These are not needed, but they are These are not needed, but they are supplied because they are very useful:supplied because they are very useful: Two-Way Selection (if-else)Two-Way Selection (if-else) Multi-Way Selection (switch)Multi-Way Selection (switch) Iteration (for) (AKA definite iteration)Iteration (for) (AKA definite iteration) Iteration (do) (similar to while loop but loop is Iteration (do) (similar to while loop but loop is

executed at least once)executed at least once)


Two-Way Selection (If-Else)Two-Way Selection (If-Else)

If (<condition>)If (<condition>)<true-block><true-block>

if (!<condition>)if (!<condition>)<false-block><false-block>

can be re-written ascan be re-written asif (<condition>)if (<condition>)

<true-block><true-block>elseelse

<false-block><false-block>


Multi-Way Selection (Switch)Multi-Way Selection (Switch)

switch (<expression>)switch (<expression>)

{{

case <constant>:case <constant>:

<block> …<block> …

}}

Most of the time, a break statement shouldMost of the time, a break statement should

be the last statement of each block.be the last statement of each block.


For LoopsFor Loops

i = 1;i = 1; // initialization// initializationwhile (i < 10)while (i < 10) // continuation condition// continuation condition{{

cout << i << “\n”;cout << i << “\n”; // block// block++ i;++ i; // update// update

}}Can be re-written asCan be re-written asFor (i = 1; i < 10; ++ i)For (i = 1; i < 10; ++ i){{

cout << i << “\n”;cout << i << “\n”;}}


Do LoopDo Loop

dodo<block><block> // executed at least once// executed at least once

while (<condition>);while (<condition>);

string done;string done;dodo{{

// some processing ….// some processing ….cout << “Done? “;cout << “Done? “;cin >> done;cin >> done;

} while (done != “yes”);} while (done != “yes”);


Break & ContinueBreak & Continue

The break statement branches control to The break statement branches control to the next statement after the logic control the next statement after the logic control structure.structure.

The continue statement branches control The continue statement branches control back to the condition in the logic control back to the condition in the logic control structure.structure.

Neither is used that much, but rarely may Neither is used that much, but rarely may be usefull.be usefull.


Loop ControlLoop Control

Counters: a variable counts the number of Counters: a variable counts the number of times to loop through data.times to loop through data.

Sentinals: a special value at the end of a Sentinals: a special value at the end of a data list signals when the loop should data list signals when the loop should stop.stop.

Flags: a boolean variable is used to record Flags: a boolean variable is used to record a condition when the loop should stop.a condition when the loop should stop.


Pseudo-codePseudo-code

A program design method where a A program design method where a program is initially written in a natural program is initially written in a natural language (eg English), then is repeated re-language (eg English), then is repeated re-written in more detail until it is written in a written in more detail until it is written in a programming language (eg C++).programming language (eg C++).


FormattingFormattingC++ does not impose any format.C++ does not impose any format.But typically:But typically:

if (<condition>)if (<condition>){{ <block><block>}}

if (<condition>)if (<condition>){{ <true-block><true-block>}}elseelse{{ <false-block><false-block>}}


FormattingFormatting

while (<condition>)while (<condition>){{

<block><block>}}

for (<initialization>; <condition>; <update>)for (<initialization>; <condition>; <update>){{

<block><block>}}


FormattingFormattingif (c1)if (c1){{ while (c2)while (c2) {{ if (c3)if (c3) {{ dodo {{ ...... } while (c4);} while (c4); }} elseelse {{ for (init; c5; update)for (init; c5; update) {{ ...... }} }} }}}}


FormattingFormatting

Be consistent with whatever style you Be consistent with whatever style you choose to make the code easier to choose to make the code easier to understand!understand!


GotoGoto

Unconditional transfer of control to Unconditional transfer of control to anywhere in the same function.anywhere in the same function.Format:Format:

… … goto <label>;goto <label>; … …<label>:<label>: … …


When to use a gotoWhen to use a goto

There may be rare and obscure reasons to There may be rare and obscure reasons to use a goto, but generally it should not be use a goto, but generally it should not be used – the result may be “spaghetti code” used – the result may be “spaghetti code” (incomprehensible logic).(incomprehensible logic).

NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER, NEVER use a goto in this course!NEVER, NEVER use a goto in this course!


Infinite LoopsInfinite Loops

A loop that never terminates on its own.A loop that never terminates on its own.A logic error.A logic error.Example:Example:

// print the values 1 to 5// print the values 1 to 5i = 1;i = 1;while (i <= 5)while (i <= 5){{ // notice the lack of// notice the lack of cout << i << “\n”; cout << i << “\n”; // incrementing i - this// incrementing i - this}} // actually prints 1s // actually prints 1s

foreverforever


Development PointersDevelopment Pointers

Use top-down design, incremental design, and pseudo-Use top-down design, incremental design, and pseudo-code.code.Think about how you would solve the problem using Think about how you would solve the problem using paper and pencil. The computer solution will probably be paper and pencil. The computer solution will probably be similar. After determining the steps you would take, then similar. After determining the steps you would take, then determine the equivalent operations in the programming determine the equivalent operations in the programming language. Then code those operations.language. Then code those operations.The patterns in the output to be achieved frequently will The patterns in the output to be achieved frequently will point you towards the logic of the program. Think about point you towards the logic of the program. Think about the operations to produce the output, the calculations the operations to produce the output, the calculations needed to do that, and finally the input needed to do needed to do that, and finally the input needed to do that. Work backwards from output to input. You know that. Work backwards from output to input. You know what you want to produce – how do you get there?what you want to produce – how do you get there?


State of the MachineState of the Machine

The state of the machine refers to all of The state of the machine refers to all of the variables used in a program – what the the variables used in a program – what the values mean at any point during the values mean at any point during the execution of that program. Understanding execution of that program. Understanding this is key to understanding the program, this is key to understanding the program, because it leads to understanding what is because it leads to understanding what is happening at any one point in the happening at any one point in the program.program.


ExamplesExamples

ch04pp05.cppch04pp05.cpp







ReadingReading

Chapter 4 & 5 cover these same concepts. Chapter 4 & 5 cover these same concepts. Reviewing them may help clarify the Reviewing them may help clarify the material.material.

16/27/2015 11:53 PM6/27/2015 11:53 PM6/27/2015 11:53 PMLogic Control Structures Arithmetic...

Documents

Transcript of 16/27/2015 11:53 PM6/27/2015 11:53 PM6/27/2015 11:53 PMLogic Control Structures Arithmetic...