chapter 4 october 22, 2013. the if statement programs make decisions if(condition){ statement(s); }...
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The If Statement OperatorMeaning = = equal to < less than greater than >= greater than or equal to != not equal toTRANSCRIPT
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