Exercise 1

1. Write a program that calculates the compounding value of an investment I with a given interest rate R and a given duration in years D.
   Here is an example of input and output of this program:

   Enter investment amount: 1500
   Enter interest rate in %: 4.5
   Enter number of years: 5
   
   OUTPUT
   
   Investment=$1500.0
   Rate=4.5%
   Number of Years=5
   Your final Amount : $1869.27
   

   Solution

   public class exer1 {
             /* program that calculates the compounding value of an investment I with a given interest rate R and a given
        duration in years D.  */
   
   
   	public static void main(String args[]) {
       /* Variables */
       
       float investmentAmount;
       float interestRate;
       float finalAmount;
       int nbYears;
       int i;
   
   	/* Program statements go here. */
   	
   		/*Reading input*/
   		System.out.print("Enter investment amount: ");
   		investmentAmount=Keyboard.in.readFloat().floatValue();		
   		System.out.print("Enter interest rate in %: ");
   		interestRate=Keyboard.in.readFloat().floatValue();		
   		System.out.print("Enter number of years: ");
   		nbYears=Keyboard.in.readInteger().intValue();
   		
   		/*Calculating the compounding investment*/
   	        finalAmount=investmentAmount;
   		for(i=0;i<nbYears;i++) {
   		    finalAmount = finalAmount + (finalAmount*interestRate/100);
   		    
   		}		
   		/*making sure there are only two digits after decimal point*/
   		finalAmount=((float)Math.round(finalAmount*100))/100;	
   		investmentAmount=((float)Math.round(investmentAmount*100))/100;
   		
   		/*printing the output*/	
   		System.out.println("Investment=$" +investmentAmount);
   		System.out.println("Rate=" +interestRate+"%");
   		System.out.println("Number of Years=" +nbYears);
   		System.out.println("Your final Amount : $" + finalAmount);
   	}
   }
   

   ---

2. Change the previous program such that the investment is either compounded every year, every 6 months, or every month, based on a given parameter P.
   Here is an example of input and output of this program:

   Enter investment amount: 1500
   Enter interest rate in %: 4.5
   Enter number of years: 5
   Interest Compounded: (1)Yearly, (2)Every 6 months, (3)Monthly:6
   (1)Yearly, (2)Every 6 months, (3)Monthly:abc
   (1)Yearly, (2)Every 6 months, (3)Monthly:33
   (1)Yearly, (2)Every 6 months, (3)Monthly:3
   
   OUTPUT
   
   Investment=$1500.0
   Rate=4.5%
   Number of Years=5
   Period: Monthly
   Your final Amount : $1877.69     
        

   Solution

   public class exer1 {
             /* program that calculates the compounding value of an investment I with a given interest rate R and a given
        duration in years D.  */
   
   
   	public static void main(String args[]) {
       /* Variables */
       
       float investmentAmount;
       float interestRate;
       float finalAmount;
       int nbYears;
       int nbPeriods;
       float intRate;
       String label;
       int i;
       char mySelection;
   
   	/* Program statements go here. */
   	
   		/*Reading input*/
   		System.out.print("Enter investment amount: ");
   		investmentAmount=Keyboard.in.readFloat().floatValue();		
   		System.out.print("Enter interest rate in %: ");
   		interestRate=Keyboard.in.readFloat().floatValue();		
   		System.out.print("Enter number of years: ");
   		nbYears=Keyboard.in.readInteger().intValue();
   		System.out.print("Interest Compounded:");
   
                   mySelection=question("(1)Yearly, (2)Every 6 months, (3)Monthly:","123");
   
   		/*Determining the number of periods, 
   		  the interest rate to use, and the label for period*/
   		switch(mySelection) {
   			case '1': nbPeriods=nbYears;
   					  intRate = interestRate;
   					  label="Yearly";
   					  break;
   			case '2': nbPeriods=nbYears*2;
   					  intRate = interestRate/2;
   					  label="Every 6 months";
   					  break;
   			case '3': nbPeriods=nbYears*12;
   					  intRate = interestRate/12;
   					  label="Monthly";
   					  break;
   			default:  nbPeriods=0;
   					  intRate = 0f;
   					  label="Unknown";
   		}
   
   		/*Calculating the compounding investment*/
   	        finalAmount=investmentAmount;
   		for(i=0;i<nbPeriods;i++) {
   		    finalAmount = finalAmount + (finalAmount*intRate/100);
   		    
   		}		
   		/*making sure there are only two digits after decimal point*/
   		finalAmount=((float)Math.round(finalAmount*100))/100;	
   		investmentAmount=((float)Math.round(investmentAmount*100))/100;
   		
   		/*printing the output*/	
   		System.out.println("Investment=$" +investmentAmount);
   		System.out.println("Rate=" +interestRate+"%");
   		System.out.println("Number of Years=" +nbYears);
   		System.out.println("Period:" +label);
   		System.out.println("Your final Amount : $" + finalAmount);
   	}
   
   	public static char question(String theQuestion, String validChoice) {
   
   		char theChoice;
   		String userInput;
   
   		do{
   			System.out.print(theQuestion);
   			userInput=Keyboard.in.readString();
   			theChoice = userInput.charAt(0);
   		} while (validChoice.indexOf(theChoice)==-1 || userInput.length()!=1);
   		return theChoice;
   	}
   }
   

   ---

3. Change the previous program such that the processing of the investment value is done in a method of a class Investment invoked many times in the main program for different values of I, R, D, and P.

   Solution

   public class exer1 {
             /* program that calculates the compounding value of an investment I with a given interest rate R and a given
        duration in years D.  */
   
   
   	public static void main(String args[]) {
       /* Variables */
       
       float investmentAmount;
       float interestRate;
       float finalAmount;
       int nbYears;
       Investment myInvestment;
   
   
   	/* Program statements go here. */
   		do {
   			/*Reading input*/
   			System.out.println("\nEnter amount 0 to quit.");
   			System.out.print("Enter investment amount: ");
   			investmentAmount=Keyboard.in.readFloat().floatValue();
   			if (investmentAmount !=0f) { 		
   				System.out.print("Enter interest rate in %: ");
   				interestRate=Keyboard.in.readFloat().floatValue();		
   				System.out.print("Enter number of years: ");
   				nbYears=Keyboard.in.readInteger().intValue();
   				System.out.print("Interest Compounded:");
   				myInvestment=new Investment(investmentAmount,interestRate,nbYears);
   				/*asking for periodicity and assigning a ratio*/
           		myInvestment.question();
           		/*printing the result for an investment*/
           		myInvestment.display();
   			}	
   		} while (investmentAmount!=0f);
   
   	}
   
   }
   
   public class Investment {
   
   /*Instance Variables*/
   
   private float investment;
   private float yearlyRate;
   private int years;
   private int ratio;
   
   	/*constructor Investment*/
   	public Investment(float sum, float percent, int duration){
   		this.investment=sum;
   		this.yearlyRate=percent;
   		this.years=duration;
   		this.ratio=1;
   	}
   
   	/*calculates the final amount based on rate and duration*/
   	public float calculate(){
   	
   		int i;
   		float finalAmount=this.investment;
   
   		for (i=0; i<(this.years*this.ratio);i++) 
   			finalAmount=finalAmount+finalAmount*(this.yearlyRate/this.ratio)/100;
   
   		return finalAmount;
   	}
   
   	/*dislays investment info*/
   	public void display(){
   
   		float finalAmount;
   		finalAmount=this.calculate();
   
   		/*making sure there are only two digits after decimal point*/
   		finalAmount=((float)Math.round(finalAmount*100))/100;	
   
   		System.out.println("Investment=$" +this.investment);
   		System.out.println("Rate=" +this.yearlyRate+"%");
   		System.out.println("Number of Years=" +this.years);
   		System.out.println("Period:" + this.periodicity());
   		System.out.println("Your final Amount : $" + finalAmount);
   	}
   	
   	/*generates a label for periodicity*/
   	private String periodicity(){
   		switch(this.ratio) {
   			case 1: return "Yearly";
   			case 2: return "Every 6 months";
   			case 3: return "Quaterly";
   			case 12:return "Monthly";
   			default: return "Unknown";
   		}
   	}
   	
   	/*asks a question to determine periodicity*/
   	public void question() {
   		String theQuestion = "(1)Yearly, (2)Every 6 months, (3)Monthly:";
   		String validChoice = "123";
   		char theChoice;
   		String userInput;
   
   		do{
   			System.out.print(theQuestion);
   			userInput=Keyboard.in.readString();
   			theChoice = userInput.charAt(0);
   		} while (validChoice.indexOf(theChoice)==-1 || userInput.length()!=1);
   
   		switch(theChoice) {
   			case '1': this.ratio=1;
   					  break;
   			case '2': this.ratio=2;
   					  break;
   			case '3': this.ratio=12;
   					  break;
   		}
   	}
   
   }
   

   ---

4. Change the previous program such that it displays the increases in the investment value after each year period.
   Here is an example of input and output of this program:

   Enter amount 0 to quit.
   Enter investment amount: 1500
   Enter interest rate in %: 4.5
   Enter number of years: 5
   Interest Compounded:(1)Yearly, (2)Every 6 months, (3)Monthly:1
   
   Year	Ratio   Investment      Increase        Amount End of Year
   1       	4.5     	1500.0          	67.5             1567.5
   2       	4.5     	1567.5          	70.54           1638.04
   3       	4.5     	1638.04         	73.71           1711.75
   4       	4.5     	1711.75         	77.03           1788.78
   5       	4.5     	1788.78         	80.49           1869.27
   
   Enter amount 0 to quit.
   Enter investment amount: 1500
   Enter interest rate in %: 4.5
   Enter number of years: 5
   Interest Compounded:(1)Yearly, (2)Every 6 months, (3)Monthly:2
   
   Year	Ratio   Investment      Increase        Amount End of Year
   1 	4.5	1500.0		33.75           1533.75
   1	4.5	1533.75       	34.51           1568.26
   2	4.5	1568.26        	35.29           1603.55
   2	4.5	1603.55        	36.08           1639.63
   3	4.5	1639.63        	36.89           1676.52
   3	4.5	1676.52        	37.72           1714.24
   4	4.5	1714.24        	38.57           1752.81
   4	4.5	1752.81        	39.44           1792.25
   5	4.5	1792.25        	40.32           1832.57
   5	4.5	1832.57        	41.24           1873.81
   

   Solution

   Add the followintg method in the Investment class:

        /*calculates the final amount based on rate and duration*/
        public float displayPerYear(){
   	
   	int i;
   	float finalAmount=this.investment;
   	int currentYear=0;
   	float initial = this.investment;
   	float finalSum;
   	float increase;
   
   	System.out.println("\nYear\tRatio\tInvestment\tIncrease\tAmount End of Year");		
   		
   	for (i=0; i<(this.years*this.ratio);i++){ 
   		if (this.ratio==1 || (this.ratio==2&&i%2==0)|| (this.ratio==12 && i%12==0))  {
   			currentYear+=1;
   		}
   		initial=(float)Math.round(finalAmount*100)/100;
   
   		finalAmount=finalAmount+finalAmount*(this.yearlyRate/this.ratio)/100;
   		finalSum=(float)Math.round(finalAmount*100)/100;
   		increase=(float)Math.round((finalSum-initial)*100)/100;
   		System.out.print(currentYear+"\t"+this.yearlyRate+"\t");
   		System.out.print(initial+"\t\t"+increase+"\t\t");
   		System.out.println(finalSum);		
   	}
   	return finalAmount;
        }
   
   In the main method, replace the statement myInvestment.display(); by the statement  myInvestment.displayPerYear();.
   
   
    Can you add in the class Investment a method that given values
        for R, D, P, and a final sum S, will
        calculated the necessary initial investment I?  
   
   Solution