chapter 4 october 22, 2013. the if statement programs make decisions if(condition){ statement(s); }...

Chapter 4

October 22, 2013

The If Statement Programs make decisions If(condition){

Statement(s); }Condition

boolean expression Evaluates to either true or false

formed using relational operators

The If StatementOperator Meaning = = equal to< less than <= less than or equal to > greater than >= greater than or equal to != not equal to

Statement single or complex Directions on what to do

Pitfalls do not use = = or ! = with decimals roundoff errors

occur because doubles cannot be exactly represented in binary

The If Statement

Only compare values of the same type

Do not confuse assignment (=) with equal to (==). Will compile but output will vary

Misplaced semicolons if(score ==21);

The If Statement

If-Else StatementContains an else clause

Excuted when if is false If(condition){ statement(s); }

else{ statement(s); }

More than one statement enclosed in { } Ex: if(temp > 5){

cout<<“Wear a coat!”<<endl; cout<<“It is cold outside”<<endl; }

Compound Statements

Nested if StatementsControls flow in 3 or more situations if statement within an if statement

If statement within an if statement If(condition){ if(condition){ statement(s); } } Ex: if(temp < 5){

if(temp< 2){ cout<<“Wear a coat”<<endl; } }

Nested if Statements

Dangling else A logic error associated with

nested if statements reason we use brackets

clarify and group

Nested if Statements

Ex: if(temp < 5)if(temp< 2)

cout<<“Wear a coat”<<endl; else cout<<“It’s hot”<<endl;

Else-if LadderDecides between three or more

actions order of if and else is very importantLast statement is executed iff the

statements before ALL fail. Ex: if(temp < 0)

else if (temp< 2) else if (temp < 4) else

if(condition){ statement(s);}

else if(condition){ statement(s);}

else{}

Else-if Ladder

Logical Operators

Used to form Boolean expressions && represents and | | represents orEvaluated based on the following

rules

True/False Operator T/F Expressions

T && T T T && F F

F && T F F && F F

Logical Operators&&- AND

OR –If example If((condition) | | (condition)){ statement(s); }

If((temp < 10) | | (wind> 20 )){ cout<<“It’s really cold!!”<<endl; }

AND –If example If((condition) && (condition)){ statement(s); }

If((temp < 10) && (wind> 20 )){ cout<<“It’s too cold to be outside”;

cout<< endl; }

Looping

Control program through iteration Repeat one or more

statements Referred to as looping

Do-whiledo {

statement(s); }while(condition);Condition

Boolean expression Determines if loop continues

Do-while executed at least once

condition executed after first loop

if condition is true then statements are executed again and condition is reevaluated.

while Statements evaluates before each loop

Can be executed 0 or more times while(condition){

statement(s); } if the condition is true then the

statements are executed and the condition is reevaluated until condition is false.

Infinite loops

Continue FOREVER Causes

misplaced semicolons missing curly brackets logic errors

Algorithms series of steps that tell how to solve a

problem usually written out first helps with structure of code helps eliminate logic errors

caused by statements that are syntactically correct but produce undesired results

Counting and Summing Counting

counts the number of values entered by the user

really counts number of loops numOfValues = numOfValues + 1;

takes values currently in variable, adds one to it and re-stores that sum in the original variable.

Counting and Summing Counting

counters variables that count need to be initialized gives it a starting value; usually 0 int i = 0;

Counting and Summing Summing

sums the values entered by a user sumOfValues = sumOfValues +

value; takes value currently stored and adds the new value and re-stores it back in sumOfValues

needs to be initialized usually zero.

Counting and Summing

Sentinel constant value the loop should end on

Easily changed

Increment and Decrement++ after a variable indicates addition of

1 numOfValues++;

adds one and re-stores new value in numOfValues

increment operator Where C++ came from

Increment and Decrement+= adds a value to a sum sumOfValues +=Value;

adds value to sumOfValues stores new value in sumOfValues.

Increment and Decrement -- subtraction of 1 from variable total --;

subtracts 1 from total stores back in total

- = subtracts a value from a total total -=value;

subtracts value from total Stores new value in total

The for Statment executes a loop for a fixed number of times

for(initialization; condition; increment){ statement(s); } initialization

performed once type counter = startingPoint;

int x = 0;

The for StatementCondition

Boolean Expression Evaluated before each loop

increment performed after each loop Advances the counter

The for Statement Initialization can be performed outside

the loop ex: int x = 0; for(; condition; increment){ statement(s); }

#include <iostream> using namespace std;

 int main(){

for ( int x = 0; x < 10;x++) { cout<< x <<endl; }

}

The bool Library Boolean variables only hold true or

false library used to implement bool type #include<bool>

using namespace std; bool Tuesday = false;

no quotations marks