<apex:page controller="sendEmail">
	<apex:messages />
	<apex:pageBlock title="Send an Email to Your 
			{!account.name} Representatives">
		<p>Fill out the fields below to test how you might send an email to a user.</p>
		<br />
		<apex:dataTable value="{!account.Contacts}" var="contact" border="1">
			<apex:column >
				<apex:facet name="header">Name</apex:facet>
				{!contact.Name}
			</apex:column>
			<apex:column >
				<apex:facet name="header">Email</apex:facet>
				{!contact.Email}
			</apex:column>
		</apex:dataTable>
    
		<apex:form >
		<br /><br />
			<apex:outputLabel value="Subject" for="Subject"/>:<br />     
			<apex:inputText value="{!subject}" id="Subject" maxlength="80"/>
			<br /><br />
			<apex:outputLabel value="Body" for="Body"/>:<br />     
			<apex:inputTextarea value="{!body}" id="Body"  rows="10" cols="80"/>           
			<br /><br /><br />
			<apex:commandButton value="Send Email" action="{!send}" /> 
		</apex:form>
	</apex:pageBlock>
</apex:page>

public class sendEmail {
	public String subject { get; set; }
	public String body { get; set; }

	private final Account account;

	// Create a constructor that populates the Account object
	public sendEmail() {
		account = [select Name, (SELECT Contact.Name, Contact.Email FROM Account.Contacts) 
				from Account where id = :ApexPages.currentPage().getParameters().get('id')];
	}

	public Account getAccount() {
		return account;
	}

	public PageReference send() {
		// Define the email
		Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage(); 

    String addresses;
    if (account.Contacts[0].Email != null)
    {
        addresses = account.Contacts[0].Email;
        // Loop through the whole list of contacts and their emails
        for (Integer i = 1; i < account.Contacts.size(); i++) 
        {
            if (account.Contacts[i].Email != null)
            {
                addresses += ':' + account.Contacts[i].Email;
            }
        }
    }

		String[] toAddresses = addresses.split(':', 0);

// add

toAddresses.add(harish.rao.salesforce@gmail.com); // u can add multiple lineslike this 

		// Sets the paramaters of the email
		email.setSubject( subject );
		email.setToAddresses( toAddresses );
		email.setPlainTextBody( body );
    
		// Sends the email
		Messaging.SendEmailResult [] r = 
			Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});   
		
		return null;
	}
}

Messaging.SingleEmailMessage message = new Messaging.SingleEmailMessage();
// Set recipients to two contact IDs.
// Replace IDs with valid record IDs in your org.
message.toAddresses = new String[] { 'test@gmail.com', 'harish@salesforce.com' };
message.optOutPolicy = 'FILTER';
message.subject = 'Opt Out Test Message';
message.plainTextBody = 'This is the message body.';
Messaging.SingleEmailMessage[] messages = 
    new List<Messaging.SingleEmailMessage> {message};
         Messaging.SendEmailResult[] results = Messaging.sendEmail(messages);
if (results[0].success) {
    System.debug('The email was sent successfully.');
} else {
    System.debug('The email failed to send: '
          + results[0].errors[0].message);
}