CC

// Currency Converter
// Class
public class CurrencyConverter {
    public Double rupee { get; set; }
    public Double dollar {get; set; }
    
    public void convertToRupee()
    {
        rupee = dollar*82.71;
    }
    
    public void convertToDollar()
    {
        dollar = rupee/82.71;
    }
}

// Visualizer
<apex:page controller="CurrencyConverter">
    <apex:form >
        <apex:pageBlock >
            <apex:pageBlockSection title="Currency Converter">
                <apex:inputText value="{!rupee}" label="Indian Rupee" />
                <apex:commandButton value="Convert to Dollars" action="{!convertToDollar}" reRender="outputPanel" />
                <apex:inputText value="{!dollar}" label="American Dollar" />
                <apex:commandButton value="Convert to Rupees" action="{!convertToRupee}" reRender="outputPanel" />
            </apex:pageBlockSection>
            <apex:pageBlockSection title="Converted Currency Values" collapsible="false">
                <apex:outputPanel id="outputPanel">
                    <apex:outputText value="Indian Rupees: {!rupee}" rendered="{!dollar != null}" />
                    <br/>
                    <apex:outputText value="American Dollars: {!dollar}" rendered="{!rupee != null}" />
                </apex:outputPanel>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>

// Calculator
// Class
public class Calculator {
    public integer firstNumber { get; set; }
    public integer secondNumber { get; set; }
    public Double result { get; set; }
    
    public void Addition() {
        result = firstNumber + secondNumber;
    }
    
    public void Subtraction() {
        result = firstNumber - secondNumber;
    }
    
    public void Multiplication() {
        result = firstNumber * secondNumber;
    }
    
    public void Division() {
        result = firstNumber / secondNumber;
    }
    
    public void Logarithm() {
        result = math.log10((Double) firstNumber) / math.log10((Double) secondNumber);
    }

    public void Square() {
        result = firstNumber * firstNumber;
    }

    public void SquareRoot() {
        result = math.sqrt(firstNumber);
    }
}

// Visualizer
<apex:page controller="Calculator">
    <apex:sectionHeader title="Calculator"/>
    <apex:form >
        <apex:pageBlock >
            <apex:pageBlockButtons location="bottom">
            	<apex:commandButton value="Addition" action="{!Addition}" reRender="result" />
               	<apex:commandButton value="Subtraction" action="{!Subtraction}" reRender="result" />
               	<apex:commandButton value="Multiplication" action="{!Multiplication}" reRender="result" />
               	<apex:commandButton value="Division" action="{!Division}" reRender="result" />
                <apex:commandButton value="Logarithm" action="{!Logarithm}" reRender="result" />
                <apex:commandButton value="Square" action="{!Square}" reRender="result" />
                <apex:commandButton value="Square Root" action="{!SquareRoot}" reRender="result" />
            </apex:pageBlockButtons>
        	<apex:pageBlockSection >
            	<apex:inputText value="{!firstNumber}" label="First Number" />
                <apex:inputText value="{!secondNumber}" label="Second Number" />
                <apex:outputText value="{!result}" label="Result" id="result" />
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>

// Temperature Converter
// Class
public class TemperatureConverter {
    public Double celsius { get; set; }
    public Double fahrenheit { get; set; }
    
    public void convertToFahrenheit() {
        fahrenheit = (celsius * 9/5) + 32;
    }
    
    public void convertToCelsius() {
        celsius = (fahrenheit - 32) * 5/9;
    }
}

// Visulizer
<apex:page controller="TemperatureConverter">
    <apex:form >
        <apex:pageBlock >
            <apex:pageBlockSection title="Temperature Converter">
                <apex:inputText value="{!celsius}" label="Celsius"/>
                <apex:commandButton value="Convert to Fahrenheit" action="{!convertToFahrenheit}" rerender="outputPanel"/>
                <apex:inputText value="{!fahrenheit}" label="Fahrenheit"/>
                <apex:commandButton value="Convert to Celsius" action="{!convertToCelsius}" rerender="outputPanel"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="Converted Temperature" collapsible="false">
                <apex:outputPanel id="outputPanel">
                    <apex:outputText value="Celsius: {!celsius}" rendered="{!fahrenheit != null}"/>
                    <br/>
                    <apex:outputText value="Fahrenheit: {!fahrenheit}" rendered="{!celsius != null}"/>
                </apex:outputPanel>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>