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I wanted to find the missing number in series so i thought a simple idea why not add all the numbers in array which are in series and hold it in one variable and then calculate the sum of series by formula `Sn=n/2(a+l)`

but while calculating the series sum i am getting some error.

public class Missing { public static void main(String[] args) { int ar [] = {1,2,3,4,5,6,7,8,9,10,11,12,13}; int sum = 0; int total=0; for(int num: ar) { sum = sum+num; } int n = ar.length; int a = ar[0]; int l =ar[ar.length-1]; total = [n/2*(a+l)]; System.out.print("The missing number is "+(sum-total)); }}

total = [n/2*(a+l)]; ……………………….(1)

This is where i am getting error.

## Answer

The first thing is in `total = [n/2*(a+l)];`

`[]`

is not valid syntax in this context. The second thing I noticed, is that your formula to calculate the sum seems odd, maybe you meant `Sn = (n * (a + l)) / 2?`

. After making those two changes the code should look as follows:

public class Missing { public static void main(String[] args) { int ar [] = {1,2,3,4,5,6,7,8,9,10,11,12,13}; int sum = 0; for(int num: ar) { sum = sum+num; } int n = ar.length; int a = ar[0]; int l =ar[ar.length - 1]; int total = (n * (a + l)) / 2; System.out.print("The missing number is "+(sum - total)); // outputs 0 which is correct nothing is missing // Now if you remove say 12 from the array // by changing the array to int ar [] = {1,2,3,4,5,6,7,8,9,10,11,0,13}; // you should get back -12 which means 12 is missing } }

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