为什么这个c-shell脚本会停止？

The script is supposed to print "Enter the nest number to add: " and keep doing this until the user enters a negative number. At which point it is supposed to print the sum of the positive numbers. However as is the loop asks for the next number one time, it is entered, and then does not ask again, the script just stops doing anything and doesn't even reach the next line within the loop.The script is supposed to print "Enter the nest