You need two loops: An outer loop to keep track of the rows, and an inner loop to keep track of the number of asterisks per row.
Right now, you have an outer loop that is keeping track of the rows. But you need to replace that cout line with an inner loop to not just print one asterisk, but to loop through printing a variable number of asterisks.
I will hant it in pseudocode, it's not too hard to figure it out by yourself:
while i != given_input_number do
while j != i do
print new line
as cscgal said you have only the outer loop, so you need to put another loop, to count how many times you have to print the asterix. In this case, at each row, you'll have to print a number of asterixes which is greater than the one before, so a while till j != i suits this matter.
poloblue I see you have 3 loops, from which 2 of them are do.... while loops. In my pseudocode I put only 2 while loops. As zeroliken said, follow the pseudocode and remember to initialize j=0 inside the first loop, so that after it prints 1 row of asterixes, to start again from 0 on the other row.