1. Member
Join Date
Feb 2009
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## Take a derivative

I want to take and display the derivative of a given input.

Java Code:
```import java.util.Scanner;
public class Derivative {

private int power;
private int coefficient;
private String variable;

public static void main(String args[]) {
Derivative d = new Derivative();
System.out.println(d.getDerivative(args[0])); 	//LINE 10

}

public void setPower(int power) {
this.power = power;
}

public int getPower() {
return power;
}

public void setCoefficient(int coefficient) {
this.coefficient = coefficient;
}

public int getCoefficient() {
return coefficient;
}

public void setVariable(String variable) {
this.variable = variable;
}

public String getVariable() {
return variable;
}

public String getDerivative(String term)
{
String derivative;
Scanner scanner = new Scanner(term);	//pass the term to the scanner
if(scanner.hasNextInt())
setCoefficient(scanner.nextInt());		//set the coefficient as the first integer
setVariable(scanner.next());			//set the variable as the next term after first integer
if(scanner.hasNextInt())
setPower(scanner.nextInt());	//set the exponent power as the next integer
int newCoefficient = power * coefficient;	//differentiate
int newPower = power - 1;
derivative = newCoefficient + variable + "^" + newPower;
return derivative;
}
}```
I tried to input 2x2, which really is 2x squared. Obviously the answer should be 4x^1, but I keep getting 02x2^-1
as a result. Whenever I call a hasNext... method with scanner, does the scanner move up a token? So that whenever I check, it moves, then I assign, and it moves, and I assign and check and etc etc. I feel like I'm doing something obviously wrong with the scanner, but I don't know how to fix it.

I also tried
Java Code:
```	public String getDerivative(String term)
{
String derivative;
Scanner scanner = new Scanner(term);	//pass the term to the scanner
setCoefficient(scanner.nextInt());		//set the coefficient as the first integer
setVariable(scanner.next());			//set the variable as the next term after first integer
setPower(scanner.nextInt());	//set the exponent power as the next integer
int newCoefficient = power * coefficient;	//differentiate
int newPower = power - 1;
derivative = newCoefficient + variable + "^" + newPower;
return derivative;
}```
But that kept telling me mismatched input.

2. You haven't configured the delimiters on your scanner. With default setup, your string has one token, '2x2', which cannot be parsed as an integer. hasNextInt() will return false, next() will return the whole token and the results will be as you see them.

3. Member
Join Date
Feb 2009
Posts
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Awesome thanks, you've been a big help in pointing out mistakes for me today. Hopefully I won't need to ask any more questions haha.

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