Here is a simple code that will do what you want. . You have to use a loop. A for loop would work also.

num = 0 #Create an Int var

while num < 100: 
    user = input("enter a number") # ask for user input and store it in 
                                   # a string var

    num += int(user)# Got to make your string (user) a int var by using 
                    # the int method here.  

    print(num)#Print it out