The program is sending users input value dollars to the function here greedyAlgorithm(dollars); // Run the greedy algorithm. Is that what you meant?

Review the lecture notes (or the lecture) to see how to use do ... while to do "something first, then checks a condition, and repeats until the condition is no longer true."

The program is sending users input value dollars to the function here greedyAlgorithm(dollars); // Run the greedy algorithm. Is that what you meant? Probably not, since the previous line is int n=round(dollars*100);, you probably meant to send n to the function.

Review the lecture notes (or the lecture) to see how to use do ... while to do "something first, then checks a condition, and repeats until the condition is no longer true.". It needs a do/while loop. Did you do mario? If so, use the same strategy. If not, review the lecture or the lecture notes, there is an example in "positive.c".