// Lab 4 Lecture


// ---------------------- Relational Operators --------------------------------
// 
// we can use comparison and relational operators to determine
// whether a condition is true or false.
//
// == is the "equal to" operator
// != is the "not equal to" operator
//  > is the "greater than" operator
//  < is the "less than" operator
// >= is the "greater than or equal to" operator
// <= is the "less than or equal to" operator

// Examples: 
// (1 == 3) will return false
// (1 > 0)  will return true
// (1 != 4) will return true

// ----------------------- IF Statements --------------------------------------

// So far we have written programs that are limited to a
// linear sequence of execution. IF statements are the first tool we 
// will learn which allows us to control the flow of our program. 
// We will now be able to control whether code gets executed or not.

// Syntax

// if (condition)
// {
//      // statements inside braces run only if the condition is true
// }

#include<iostream>
#include<fstream>

using namespace std;

int main()
{
	ifstream fin;
	int num1 = 10;
	int num2 = 5;
	int num3 = 20;
	int grade = 90;
	char lettergrade;

    // Here is a simple if statement using curly brackets.
    // Good style dictates that we should indent everything
    // inside of the if statement (PLEASE DO THIS).

	if (num1 < grade)  // (10 < 90)
	{
		cout << num1 << " is less than " << grade << endl;
		num1 += 5;
		cout << "num 1 is now " << num1 << endl << endl;
	}

	// if you only have one statement inside the IF statement you
	// do not need curly braces

	if (num1 > num3)   // (10 > 20)
		cout << num1 << " is greater than " << num3 << endl;


	// you can also fine tune your if statements by nesting them

	if (num1 != num3)  // (10 != 20)
	{
		cout << num1 << " is not equal to " << num3;

		if(num1 < num2)  // (10 < 5)
		{
			cout << " and " << num1 << " is less than " << num2 
			     << endl << endl;
		}

		if(num1 > num2)  // (10 > 5)
		{
			cout << " and " << num1 << " is greater than " << num2 
			     << endl << endl;
		}
	}

// ------------------------- Common Mistakes ----------------------------------

	// Do NOT put a semicolon after your IF statement.
    // This mistake will cause your IF statement to not work.
	if (num1 == num3);
		cout << num1 << " is equal to " << num3 << endl << endl;

	// Another common mistake.
	// = is the assignment operator.
	// == is the comparison operator.
	if (num3 = num1)  
		cout << num3 << " is equal to " << num1 << endl << endl;


	// Another tip is to be very careful with your braces. It is very
	// easy to forget one, or add an extra brace on accident. This is
	// where using good style is crucial to helping you avoid wasting
	// time debugging syntax errors.

	
// ---------------------- ELSE IF Statements ----------------------------------

	// The ELSE IF statement are pretty straight forward.
	// If your IF statement is false, then it will check the following
	// ELSE IF statement's condition. This will repeat until one
	// of the statement's condition is true, or if they are all false
	// none of the statements will be executed.

	// However, if several conditions are true, it will only execute the
	// first true condition it comes to, skipping the rest.

	// Example, all are true but only the first will execute.

	if (1 == 1)
	{
		cout << "First" << endl << endl;
	}
	else if (2 == 2)
	{
		cout << "Second" << endl << endl;
	}
	else if (3 == 3)
	{
		cout << "Third" << endl << endl;
	}

// --------------------- ELSE Statements --------------------------------------

	// ELSE Statements

	// the "else" statement will only execute if
	// all of the previous IF and ELSE IF statements
	// were false.

	if (100 <= 4)
	{
		cout << "will never execute" << endl << endl;
	}
	else
	{
		cout << "Inside Else" << endl << endl;
	}

	// Here is an example of IF-ELSE IF statemnts
	
	grade = 95;

	if (grade < 60)
	{
		lettergrade = 'f';
	}
	else if (grade < 70)
	{
		lettergrade = 'd';
	}
	else if (grade < 80)
	{
		lettergrade = 'c';
	}
	else if (grade < 90)
	{
		lettergrade = 'b';
	}
	else
	{
		lettergrade = 'a';
	}

	cout << "Your final grade is: " << lettergrade << endl << endl;
	
	
// ----------------------- Logical Operators ----------------------------------

	// && and || and ! are logical operators and can be used to evaluate
	// logical expressions.
	

	// && - Logical AND operator will return true only when both sides are true

	// true  && true  = true
	// true  && false = false
	// false && true  = false
	// false && false = false

	
	if ( 1 < 3 && 5 == 5)
		cout << "both expressions are true" << endl << endl;


	// || - Logical OR operator will return true if either of the sides is true

	// true  || true  = true
	// true  || false = true
	// false || true  = true
	// false || false = false

	if ( 10 == 5 || 1 != 0)
		cout << "one or both of the expressions are true" << endl << endl;

	// ! - NOT operator will flip the logical value.

	// !true  = false
	// !false = true

	if ( !(1 == 5) )
		cout << "NOT operator flipped a false operation to true." << endl << endl;

		
// ----------------------- File Error Detecting ----------------------------------
	
    // On a final note. Always use an if statement to check if you 
	// successfully opened a file or not. If the file successfully opens it will 
	// return 'true', otherwise 'false'. Therefore, we can use the NOT operator to
	// detect "if NOT successful" and terminate the program.
	
	fin.open("results.txt");

	if (!fin) 
	{
		cout << "ERROR - Failed to open file. Terminating program.\n";
		 return -1;  // terminate program
	}


	return 0;
}