GrPA 1 - While Loop - GRADED

Course: Jan 2026 - Python

• Use while only when the number of iterations is indefinite.
• If you can term the steps as do n times, do once for each item, etc. use for loop instead.
• If you can only term the steps as do until something happens. Like when user inputs 10.

• Method 1
• Method 2

python
Run Inline
# method 1
a = input()
while a != terminal_word: # opposite of the terminal condition
    # do something with a
    a = input() # take the next a

# method 2
while True: # loop forever
    a = input()
    if a == terminal_word: # the terminal condition
        break
    # do something with a

1. Accumulation - Accumulating a final result
   1. sum_until_0: Continuously read integers from standard input until you receive a zero. Print the sum of these integers.
   2. total_price: Continuously read pairs of integers from standard input, representing the quantity and price of items, until you receive the string "END". Print the total price of all items.
2. Filtering - Selecting based on a criterion
   1. only_ed_or_ing: Continuously read strings from standard input until you encounter the word "STOP" (case insensitive and not included in the output). Print only those strings that end with "ed" or "ing" (case insensitive).
   2. reverse_sum_palindrome: Continuously read positive integers from standard input until you encounter a "-1"(not included in the output). Print only those integers for which the sum of the number and its reverse is a palindrome.
3. Mapping - Applying the same operation to different items
   1. double_string: Continuously read lines from standard input until an empty line is encountered. Print each line repeated twice.
   2. odd_char: Continuously read strings from standard input until you encounter a string ending with a "."(include that string with the "." in the output). Extract characters at odd positions (starting from 1) of each line, and print the results in a single line separated by spaces.
4. Filter and Map - Applying an operation to selected items
   1. only_even_squares: Continuously read numbers from standard input until "NAN" is encountered. Print the square of each number only if it is even.
5. Filter and Accumulate - Accumulating a result with selected items
   1. only_odd_lines: Continuously read lines from standard input until "END"(not included in the output) is encountered. Create a string by prepending only the odd lines (starting from 1) with a newline character in between, and print the result which will be the odd lines in reverse order.

python
Run Inline
if task == "sum_until_0":
    total = 0
    n = int(input())
    while ...: # the terminal condition
        ... # add n to the total
        ... # take the next n form the input
    print(total)

elif task == "total_price":
    total_price = 0
    while ...: # repeat forever since we are breaking inside
        line = input()
        if ...: # The terminal condition
            break
        quantity, price = line.split() # split uses space by default
        quantity, price = ... # convert to ints
        ... # accumulate the total price
    print(total_price)
elif task == "only_ed_or_ing":
    ...

elif task == "reverse_sum_palindrome":
    ...

elif task == "double_string":
    ...

elif task == "odd_char":
    ...

elif task == "only_even_squares":
    ...

elif task == "only_odd_lines":
    ...

Public Tests ( 16/16 )

Case 1

text
sum_until_0
5
3
2
0

text
10

text
10

Case 2

text
sum_until_0
10
-5
5
0

Case 3

text
total_price
2 50
1 100
3 30
END

text
290

text
290

Case 4

text
total_price
5 10
2 20
END

text
90

text
90

Case 5

text
only_ed_or_ing
Reading
completed
running
start
END
STOP

text
Reading

completed

running

text
Reading

completed

running

Case 6

text
only_ed_or_ing
opened
close
stopped
move
ingested
STOP

text
opened

stopped

ingested

text
opened

stopped

ingested

Case 7

text
reverse_sum_palindrome
56
99
32
-1

text
56

32

text
56

32

Case 8

text
reverse_sum_palindrome
12
19
23
34
87
-1

text
12

23

34

text
12

23

34

Case 9

text
double_string
hello
world

text
hellohello

worldworld

text
hellohello

worldworld

Case 10

text
double_string
foo
bar
baz

text
foofoo

barbar

bazbaz

text
foofoo

barbar

bazbaz

Case 11

text
odd_char
Hello
WORLD.

text
Hlo WRD

text
Hlo WRD

Case 12

text
odd_char
This
is
a
sample
sentence.

text
Ti i a sml snec.

text
Ti i a sml snec.

Case 13

text
only_even_squares
3
4
5
NAN

text
16

text
16

Case 14

text
only_even_squares
2
7
8
NAN

text
4

64

text
4

64

Case 15

text
only_odd_lines
one
two
three
four
END

text
three

one

text
three

one

Case 16

text
only_odd_lines
line1
line2
line3
END

text
line3

line1

text
line3

line1

Private Tests ( 16/16 )

Case 1

text
sum_until_0
100
200
300
0

text
600

text
600

Case 2

text
sum_until_0
-1
-1
2
0

text
0

text
0

Case 3

text
total_price
1 1
2 1
3 1
END

text
6

text
6

Case 4

text
total_price
3 4
4 5
END

text
32

text
32

Case 5

text
only_ed_or_ing
tracked
jumped
book
coding
none
STOP

text
tracked

jumped

coding

text
tracked

jumped

coding

Case 6

text
only_ed_or_ing
raced
coded
running
STOP

text
raced

coded

running

text
raced

coded

running

Case 7

text
reverse_sum_palindrome
21
123
456
-1

text
21

123

text
21

123

Case 8

text
reverse_sum_palindrome
44
55
77
-1

text
44

text
44

Case 9

text
double_string
test
example

text
testtest

exampleexample

text
testtest

exampleexample

Case 10

text
double_string
python
programming

text
pythonpython

programmingprogramming

text
pythonpython

programmingprogramming

Case 11

text
odd_char
Programming
in
python
is
fun.

text
Pormig i pto i fn

text
Pormig i pto i fn

Case 12

text
odd_char
Make
it
work.

text
Mk i wr.

text
Mk i wr.

Case 13

text
only_even_squares
9
10
12
NAN

text
100

144

text
100

144

Case 14

text
only_even_squares
15
22
27
NAN

text
484

text
484

Case 15

text
only_odd_lines
A
B
C
D
END

text
C

A

text
C

A

Case 16

text
only_odd_lines
one
two
three
four
five
END

text
five

three

one

text
five

three

one

💻 IITM Official Solution

python
Run Inline
# Note this prefix code is to verify that you are not using any for loops in this exercise. This won't affect any other functionality of the program.
with open(__file__) as f:
    content = f.read().split("# <eoi>")[2]
if "for " in content:
    print("You should not use for loop or the word for anywhere in this exercise")

# This is the first line of the exercise
task = input()
# <eoi>

if task == "sum_until_0":
    total = 0
    n = int(input())
    while n != 0: # the terminal condition
        total += n # add n to the total
        n = int(input()) # take the next n form the input
    print(total)

elif task == "total_price":
    total_price = 0
    while True: # repeat forever since we are breaking inside
        line = input()
        if line == "END": # The terminal condition
            break
        quantity, price = line.split() # split uses space by default
        quantity, price = int(quantity), int(price) # convert to ints
        total_price += quantity * price # accumulate the total price
    print(total_price)
elif task == "only_ed_or_ing":

    word = input()
    while word.lower() != "stop":
        if word.lower().endswith("ed") or word.lower()[-3:]=="ing": # both ways of doing it
            print(word)
        word = input()

elif task == "reverse_sum_palindrome":

    num = int(input())
    while num !=-1:
        rev_num = int(str(num)[::-1])
        num_sum = num+rev_num
        if str(num_sum) == str(num_sum)[::-1]:
            print(num)
        num = int(input())

elif task == "double_string":

    line = input()
    while line != "":
        print(line*2)
        line = input()

elif task == "odd_char":

    line = input()
    while line[-1] != ".":
        print(line[::2],end=" ")
        line = input()
    print(line[::2])

elif task == "only_even_squares":

    while True:
        line = input()
        if line == "NAN":
            break
        num = int(line)
        if num % 2 == 0:
            print(num * num)

elif task == "only_odd_lines":

    result  = ""
    line_no = 1
    while True:
        line = input()
        if line == "END":
            break
        if line_no%2:
            result = line + "\n" + result
        line_no+=1
    print(result)

💻 My Submitted Code

python
Run Inline
# Note this prefix code is to verify that you are not using any for loops in this exercise. This won't affect any other functionality of the program.
with open(__file__) as f:
    content = f.read().split("# <eoi>")[2]
if "for " in content:
    print("You should not use for loop or the word for anywhere in this exercise")

# This is the first line of the exercise
task = input()
# <eoi>

if task == "sum_until_0":
    total = 0
    while True:
        n = int(input())
        if n == 0:
            break
        total += n
    print(total)

elif task == "total_price":
    total_price = 0
    while True:
        line = input()
        if line == "END":
            break
        quantity, price = line.split()
        quantity, price = int(quantity),int(price)
        total_price += quantity * price
    print(total_price)
elif task == "only_ed_or_ing":
    while True:
        word = input()
        if word.lower() == "stop":
            break
        w = word.lower()
        if w.endswith("ed") or w.endswith("ing"):
            print(word)

elif task == "reverse_sum_palindrome":
    while True:
        n = int(input())
        if n == -1:
            break
        rev = int(str(n)[::-1])
        s = n + rev
        if str(s) == str(s)[::-1]:
            print(n)

elif task == "double_string":
    while True:
        line = input()
        if line == "":
            break
        print(line * 2)

elif task == "odd_char":
    result = []

    while True:
        line = input()

        if line.endswith("."):
            result.append(line[::2])
            break
        result.append(line[::2])

    print(" ".join(result))

elif task == "only_even_squares":
    while True:
        line = input()
        if line == "NAN":
            break
        n = int(line)
        if n % 2 == 0:
            print(n*n)

elif task == "only_odd_lines":
    lines = []
    index = 1

    while True:
        line = input()

        if line == "END":
            break

        if index % 2 == 1:
            lines.append(line)

        index += 1

    lines.reverse()

    print("\n".join(lines))