Condition of square root algorithm (Newton's method)
Try calculating the square root if 1e-100 with the changed loop condition and see what result you get. Then try calculating the square root of 1e100. Do you run into any problems?

This is numerical mathematics, limits won’t work well. Print out the value of t -c/t and check whether it actually converges, and check if it converges to 0. For some different values if c.

From a wiser man than me: The problem are not the things we don’t know. The problem are the things we know that ain’t so.