How can sum one run

Chef junior recently learnt to code. Today he successfully compiled a code which takes in a stream of integers and prints the running sum. for example, if the input is $1,2,3,4,5$ then his prgram prints $1,3,6,10,15$. Chef junior's code was very simple, he initialised a variable $sum$ with $0$ and on reading an integer input he simply added it to the $sum$ variable and printed it. His co