Let’s clean it up:
var j = 0;
var t = 0;
do {
j++;
t += j;
} while (j < 5);
alert(t);
If you manually expand this (and I will), this is the equivalent code without loops:
var j = 0;
var t = 0;
j++; // j = 1
t += j;
j++; // j = 2
t += j;
j++; // j = 3
t += j;
j++; // j = 4
t += j;
j++; // j = 5
t += j;
alert(t);
Condensing this:
var t = 0;
t += 1;
t += 2;
t += 3;
t += 4;
t += 5;
alert(t);
Which results in:
var t = 1 + 2 + 3 + 4 + 5;
alert(t);
And I think you can do simple arithmetic:
var t = 15;
alert(t);
solved Why does “t” in “do{j++; t+=j;}while(j<5);" return 15? [closed]