How to fix “exception in thread main java.lang.stringindexoutofboundsexception string index out of range” errors

I'm trying to recreate the game of mastermind except a simplified version. I've been stuck on this one error and I don't know how to fix it.

String combo = "";
int plus = 0;
String in = "";
int right = 0;
int numbers = 6;
int length = 4;
int tries = 10;
int[] guessNums = new int[numbers];
int[] comboNums = new int[numbers];
rules();

combo = guesses();
for(int i = 0; i < length; i++)
{

if(in.charAt(i) == combo.charAt(i))

{

right++;

}

guessNums[in.charAt(i)-49]++;

comboNums[combo.charAt(i)-49]++;

}
for(int i = 0; i < numbers; i++)

{

while(comboNums[i] > 0 && guessNums[i] > 0)

{

plus++;

comboNums[i]–;

guessNums[i]–;

}

}

String reset =  “\u001B[0m”;

System.out.print(“\t”);

String a = “” + right;

printRed(a);

System.out.println(" " + reset + “” + plus);

System.out.println(“\n”);
tries–;

return(right == length);

it says the error is in line if(in.charAt(i) == combo.charAt(i)).

#java #arrays #string #methods