[spoiler title=”Lesson Video”]
Direct Download of Video (For mobile / offline viewing)(right click > save target as)


[/spoiler]

[spoiler title=”Lesson Source Code”]


#include <iostream>
#include <cmath>
using namespace std;
 
 
int main(){
 
  //   ==  Double equals sign  -- boolean comparison operator  
  // boolean = type of variable that can only hold true or false
  // || or, && and, > Gt, <lt , >=, < =, ! not, !=,  
  // bool -- Type
 
  //bool isTaken = false;
  //char c = ' ';
 
  //if ( isTaken ){
  //  cout << "This seat is already purchased" << endl;
  //}
  //else{
  //  cout << "This seat costs $12 would you like to purchase this seat? Y/N" << endl; 
  //  cin >> c;
  //  if (c == 'Y'){
  //    isTaken = true; 
  //    cout < < "Thank you for your purchase";
  //  }
  //  else{
  //    cout << "Thanks for your interest";
  //  }
 
  //}
 
  int i = 0;
  if ( 1 < 7 || 9 < 6  ){ 
    cout << "Is True" << endl;
    i += 9;
  }
  else{
    cout << "Is false" << endl;
  }
 
  cout << i;
 
 
  system("PAUSE");
  return 0;
}


[/spoiler]

Homework: http://beginnerscpp.com/forums/index.php/topic,60.0.html



If Statements
If statements are used to determine the course that our program will run in, based off whether a condition evaluates to being true, or false. The statement of if has 2 parts. if and the condition that it’s checking (which can have many parts). A simple if statement might look something like this:

if (myNumber == 2){
    myNumber +=5;
}

or they can be much more complex, like this

int multiplier=3, manaCost=17, healthCost=14, intellect=27, playerCurrentHealth=5, playerCurrentMana=15, damage =0;
bool isStunned=false;
if(intellect >=20 && playerCurrentMana >= manaCost && playerCurrentHealth >= healthCost && !isStunned){
     damage = multiplier*intellect;
}
else if(isStunned){
    cout < < "You are stunned. " << endl;
}
else{
    cout << "Insufficient health and / or mana to cast." << endl;
}

In the first example we are simply checking if a number is equal to the number 2. Once we determine that is true, we add 5 to the number. The second example is something you might see in a game development scenario. A user is goes to cast a spell, there needs to be checks made against current values, and those are passed over to our if statements. We need for ALL of those conditions to be true for the spell to be cast (the user needs enough intellect to understand the spell, they need both mana and health, and they cannot be stunned) if any of those are not true, it will be passed to the else if (and then evaluated for truth there) then passed to else if that is not true either.

If Statement Flowchart
Classically if statements were represented (in flowcharting) as diamond layed on its side, with lines coming from the edges diagonally to illustrate that there were two paths that can be taken from an if statement (symbolizing an if and an else). While this is technically correct, it does lead to some questions among beginners for instance the following is VALID code

if(myNumber ==5){
   myNumber +=2;
}

cout < < "The value of myNumber is: " << myNumber;

In the example above you will notice that there is no “else” attached to this if. So the earlier example showing two distinct “branches” might not always be clearly represented in code. A way that I’ve seen some beginners cope with this confusion is by putting in Null else statements (else statements that are just placeholders) and I am against this for 2 reasons:

  1. It adds length to your code
  2. It adds no functionality to your code

Here’s an example of something a student sent me that was along those lines.

...

if( startingCash >= 5000 ){
     interestRate=5;
}
else{
    //placeholder
}
...

As you can see there is no functionality gained from this type of code.


Scope
Scope is essentially the “lifespan” of a variable. When a variable is declared within a specific scope it “dies” (is destroyed) with that scope. This is useful and dangerous at the same time. Scopes will become more important when we get into loops. Below is a short example showing a variable declared in a scope and being unavailable outside of the scope:

if ( true ){
    int myNumber = 1;    //Declared in scope
}     //Gets destroyed here
cout < < myNumber;     //This command will fail since myNumber was destroyed at the end of the scope established by the if statement

Boolean Comparison Operators

  • == (Equal to)
  • != (Not Equal To)
  • ! (Not (typically used with bool variables))
  • > (Greater Than)
  • < (Less than)
  • >= (Greater than / Equal to)
  • <= (Less Than / Equal to)
  • || (Or)
  • && (And)

Please note, the listing above is not a complete list of operators, but it will encompass the scope of what we will be learning in this course. There are other operators called “Bitwise operators” that you can read about if you choose, though you will likely not need to use them for quite some time.

[spoiler title=”Lesson Video”]
Direct Download of Video (For mobile / offline viewing)(right click > save target as)


[/spoiler]

[spoiler title=”Lesson Source Code”]


#include <iostream>
using namespace std;
 
 
int main(){
 
  //9>8 == true == 1, 1>7 ==false
 
  //nested if's
  //if inside of an if
  //Homework:  If the salesperson made less than 4000 in a month, they do not get any bonus
  //Fix all the if statements so that they work properly
  //Bonus: If the person made over 15000, they get a 100 bonus added to their check after commision has been factored in.
        // ==, < , > < !=, >=, < =, !, &&, ||
 
 
 
  double pay = 0.0, comission = 0.0, sales = 0.0;
  cout << "Enter the salesperson's sales for the month: ";
  cin >> sales;
 
  if (sales > 4000 && sales &lt;5000){
    comission = 0.01;
  }
  else if (sales >5000 && sales < 6000){
    comission = 0.02;
  }
  else if (sales >6000 && sales < 7000){
    comission = 0.03;
  }
  else if (sales >7000 && sales < 8000){
    comission = 0.04;
  }
  else if (sales >8000 && sales < 9000){
    comission = 0.05;
  }
  else{
    comission = 0.08;
  }
 
  pay = 400;
 
 
  //cout << "Pay = " << pay << " -- comission = " << comission << "\n\n";
  cout << "\nThe salesperson's pay for the month is: " << (pay*(1 + comission)) << endl;
 
  system("PAUSE");
  return 0;
}


[/spoiler]

Homework: http://beginnerscpp.com/forums/index.php/topic,61.0.html



Nested If Statements
Despite the title of this lesson, I did very little in the way of showing you nested if statements, and the reason why I opted to teach it this way was because I wanted to show that intelligent program design can get away from nesting. Sometimes nesting is unavoidable, and for those cases the following syntax remains true

if(firstConditional){
     if(secondConditional){
          //stuff Happens here
     }
     else{
          //Stuff can also happen here
     }
}
else{
     //If the first if was false
}

The only thing that I can advise you on when it comes to nested if statements is that you should be EXTREMELY strict when it comes to your indenting. Furthermore, some people like to document their code to remind them which if statement they are in, however I find this type of commenting somewhat excessive. A comment here and there to remind us what something does, or what we’re testing is fine, but when you see something like this, it’s a bit excessive.

if( condition ){//First if statement
     if( condition2){//inside second if statement
            ...
      }//end inner if
}//end first if
else{//outer else statement
     ...
}//end else

While I understand the intention of the person that made the comments, it actually adds to confusion over stating the implied usage on a single line like this:


//The following if statements will determine .... and if not they will go to the else and ...
if( condition ){
     if( condition2){
            ...
      }
}
else{
     ...
}


Topics discussed: If statements, simple if syntax, variable output, if else structure.

Source Code from lesson:

#include <iostream>

using namespace std;   
 
 
int main(){

    double accountBalance=5000.0, withdrawAmount=0;
    
    cout << "How much money would you like to withdraw? ";
    cin >> withdrawAmount;
    
    if(withdrawAmount > accountBalance){
        cout << "Error: The amount you tried to take out is greater than your current balance.";
    }
    else if(withdrawAmount > 1000){
        cout << "It looks like you're trying to take out a lot of money, call your bank to confirm";
    }
    else{
        cout << "You withdrew: " << withdrawAmount << " -- Your remaining account balance is:  " << accountBalance - withdrawAmount;
    }
    
    //  if(conditional) --Structure
    //  IF - (if this is true) -- do some stuff
    //  Else if - if the first condition wasn't true, check to see if this is true
    //  else -- If none of the things we checked are true
    //  Boolean operators
    //  == (equal to) -- ||(or) -- != (Not Equal To) -- ! (not) -- < (less than) -- > (greater than), 
    //  <=, >=(less than / equal to and greater than / equal to)
    //  true -- false -- bool (variable type that contains true or false)
    
    
     return 0;       
}


If statements
If statements are the backbone of simple decision making in object oriented programming languages. The if statement checks one or more statements for a boolean(true or false) value. Their basic structure is as follows


if (condition){
    //if the above is true
}

//optional

else{ //or elseif(condition){
     //if the "if" statement above was not true
}

Below are some examples of these statements:


If statement examples:


// Examples
// Example 1

int i=9;
if (i == 9){
     cout<< "This condition is true";
} //this statement should be true

in the above example the if statement compares (using the == operator) the integer value of i, to the number 9. In that case the statement if (i==9) is true, thus the code inside the brackets is executed.


// Example 2

int i=9;
if ( i != 8){
     cout << "This condition is also true"; 
}

In the example above we see that the contents of i (which is 9) is being compared to 8 with != which means “does not equal” or “is not equal to”. Since 9 does not equal 8, the contents of the if statement will execute.


//Example 3
int i=9;
if (i == 8){
     cout << "The if statement here won't be displayed"; 
}
else{
     cout << "This will be displayed";
}


In the final above example we are checking to see if the value of i (9) is equal to 8, in this case it is no. So everything from the bracket after the conditional until the subsequent closing bracket is skipped over. Once the word else is seen, it will execute anything in the brackets after the else, unless there are further if statements to be evaluated inside the if.


Boolean operators
Below is a brief listing of the boolean operators used in testing conditionals and what each of them mean, there will be specific usage examples of each later on in the series.

  • == : Is equal to
  • != : Is not equal to
  • > : Is greater than
  • >= : Is greater than or equal to
  • < : Is less than
  • <= : Is less than or equal to
  • ! : Is not
  • && : And
  • || : Or