It is often set to zero initially, because it serves as a variable slowly adding the rest of the numerical values.
E.g. If you want the sum of 1,2,3,4,5 it would be: sum = 1+2+3+4+5. If you use any other initial value for sum, let's say 1, the sum would be calculated as 1+1+2+3+4+5
Just a quick quiz to see if you really understand now:
Suppose now we are running loops to calculate the product of an array of numbers,
What value should we initialize the variable for storing temp products as?
There is a good reason behind initializing sum to 0.
So basically what is expected from a variable named in this manner might be to store the sum of a collection of data.
So just assume you have a list with values - [1,2,3,4,5] and you want to get the sum. A classic way is iterating through all of the elements and add each number to the variable sum.
So in runtime sum would undergo to changes like this
sum = (((((1) + 2) + 3) + 4) + 5)
//what i want to express with bracket are the iterations.
And finally sum would store 15 in it.
But we need to initialize it before using. If we initialized with 1 or another instead of 0 the sum would have a different value - in this case 16.
#version Sum = 0
sum = 0 + (1+2+3+4+5)
#version sum = 1
sum = 1 + (1+2+3+4+5)
= 1 + 15
Hope you got it.