Chapter 6 Repetition Control Instructions¶

Keynote¶

6.1 Repetition Control Instructions (Zei dah an si?)¶

Program chungah statement (tuah dingmi) pawl a nawn in tuah ṭhan lengmang kan duh tikah hman a si. Repetition control instruction phun hnih a um:

while
for

Language dang (C, C++, Java) bantuk in do-while loop hi Python ah a um lo.

while loop cu condition a hman (true) chung paoh kha instruction a tuah ṭhan lengmang. Phun hnih in kan hman khawh:

1. The `while` Loop¶

while loop cu condition a hman (true) chung paoh kha statement pawl a tuah ṭhan lengmang. Condition kha thil tuah hlan ah a check hmasa, cucaah entry-controlled loop tiah auh a si.

A Umtu Ning (Syntax):

Phun hnih in while loop hi hman khawh a si:

A. A Umtu Ning Pang (Basic Structure)

while condition:
    # Loop chungah tuah dingmi
    statement1
    statement2
    # Condition kha a donghnak ah False a si a hau,
    # lo cun a tawp ti lomi (infinite loop) a chuak lai!

while loop 2

while condition :
    statement1 
    statement2
else :
    statement3
    statement4

else block hi hman a hau hrimhrim lo (optional). Asinain kan hman ahcun, condition a 'false' tikah a chung i statement pawl kha a tuah lai.
break statement hman in while loop kha kan hrawh/donghter sual ahcun, else block kha a tuah lai lo.

while loop

while condition :
    statement1 
    statement2

for cu string, tuple asiloah list bantuk sequence (thil tlar) chung i element pawl pakhat hnu pakhat lakin tuah ṭhan lengmang nak ah hman a si. Phun hnih in a um:

for var in list : 
    statement1 
    statement2

for var in list : 
    statement1 
    statement2
else :
    statement3
    statement4

Loop a kal fatin var kha list chung in a changtu value (hmet) pek a si.
list hmun ah string, tuple, set asiloah dictionary zong hman khawh a si.
else block cu hman a hau hrimhrim lo (optional). Kan hman ahcun, break hman in loop kan hrawh lo poh ahcun else chung i statement pawl kha a tuah lai.

6.2 While loop hman ning¶

while loop hi a tanglei thil sining pathum ah hman khawh a si:

Condition a hman (True) chung paoh statement pawl tuah ṭhan lengmang.
Statement pawl kha kan duh zat tiang (voi zeizat dah ti hngalh cia in) tuah ṭhan lengmang.
String, list, le tuple chung i element pawl lakin kal.

Condition a hman chung paoh statement tuah ṭhan lengmang kan ti tikah, statement kha voi zeizat dah tuah a hau lai ti a hngalh cia lomi caah hman a si.

num = int(input('Enter a number: '))
while num != 5 :
    print(num, num * num)
    num = int(input('Enter a number: '))

* Input ah 5 na ṭial tikah loop cu a dong lai.

Statement pawl kha voi zeizat dah tuah ding ti hngalh cia in (finite number of times) tuah ṭhan lengmang nan while loop kan hman khawh.

count = 0
while count < 10 :
    print(count, count * count, count * count * count)
    count += 1

while loop cu index nambat (index value) hman in string, list, asiloah tuple chung i thil ummi pawl lakin kal nan hman khawh a si, a tanglei program ah kan hmuh bantuk in:

s = 'Mumbai'
lst = ['desert', 'dessert', 'to', 'too', 'lose', 'loose'] 
tpl = (10, 20, 30, -20, -10)
i = 0
while i < len(lst) :
    print(i, s[i], lst[i], tpl[i])
    i += 1

Theih ding (Note):

Hi program ah hin tpl (tuple) hi element 5 lawng a ngei, asinain lst (list) hi element 6 a ngei. Loop hi lst sau (length) chung a kal lai caah, a donghnak ah tpl index a tlauh sual (IndexError) kho.

Set asiloah Dictionary chung i thil pawl cu index nambat hman in lak khawh an si lo caah, for loop hman hi a ṭha deuh.

Cunglei i while loop hman ning pathum kan hmuhmi chung ah, a pakhatnak (voi zeizat dah tuah ding hngalh cia lo, condition hman chung paoh) hi hman a tam bik a si. A dang pahnih cu for loop hman in tuah a tlangpi a si.

6.3 For loop hman ning¶

for loop cu a tanglei thil sining pahnih ah hman khawh a si:

Statement pawl kha voi zeizat dah tuah ding ti hngalh cia in (finite number of times) tuah ṭhan lengmang.
string, list, tuple, set asiloah dictionary chung i thil ummi pawl lakin kal.

Statement pawl kha voi zeizat dah tuah ding ti hngalh cia in tuah ṭhan lengmang kan duh tikah, a chungah a um ciami function range() hi hman a si.

range() function nih integer (nambat tling) tlar a chuah.

range(10) - 0 in 9 tiang nambat a chuah.
range(10, 20) - 10 in 19 tiang nambat a chuah.
range(10, 20, 2) - 10 in 19 tiang, 2 in karh in a chuah (10, 12, 14...).
range(20, 10, -3) - 20 in 9 tiang, 3 in zor in a chuah (20, 17, 14...).
Theih ding: range() nih float (point nambat) tlar a chuah kho lo.

A tlangpi in, range(start, stop, step)

Hi nih hin integer nambat tlar kha start in a thawk lai i stop tiang a kal lai (asinain stop nambat taktak kha a tel lo/exclusive), cun step zat in a karh/zor lai.

range() hman in nambat tlar kan chuahmi pawl kha for loop hman in kan lak khawh.

for i in range(1, 10, 2) :
    print(i, i * i, i * i * i)

A for loop is very popularly used to iterate through a string, list, tuple, set or dictionary, as shown below.

for char in 'Leopard' :
print(char)
for animal in ['Cat', 'Dog', 'Tiger', 'Lion', 'Leopard'] :
print(animal)
for flower in ('Rose', 'Lily', 'Jasmine') :
print(flower)
for num in {10, 20, 30, -10, -25} :
print(num)
for key in {'A101' : 'Rajesh', 'A111' : 'Sunil', 'A112' : 'Rakesh'} :
print(key)

Pakhatnak for loop ah khan, loop a kal fatin char kha string chung in a changtu value (cafang) pek a si.

Cu bantuk ṭhiamṭhiam in, pahnihnak, pathumnak le palinak for loop ah, loop a kal fatin animal/flower/num kha list/tuple/set chung in a changtu value pek an si.

Theih ding: A donghnak for loop ah dictionary key (a bi) lawng kan chuah (print) kha na hmuh lai. A value (a man) chuah, asiloah a key le a value chuah ṭi kha cu Chapter 11 ah kan cawng te lai.

for loop hman in thil tlar chung kan kal lio ah, a umnak hmun (index) zong hngalh chih kan duh ahcun, a tanglei bantuk in a chungah a um ciami enumerate() function hi hman ding a si:

lst = ['desert', 'dessert', 'to', 'too', 'lose', 'loose'] 
for i, ele in enumerate(lst) :
    print(i, ele)

6.4 break le continue¶

break le continue statement pawl hi while le for he hman khawh an si.
break statement nih else block tuah lo in loop kha a donghter/hrawh.
continue statement nih block chung i statement dang pawl kha a hlut (skip) i, loop a changtu iteration ah a kal colh.

6.5 Loop i Else Block¶

while loop i else block cu, loop kha a pang tein a dih (normally terminated) lawngah thil tuah ter kan duh i, break hman in a tawp tikah tuah ter kan duh lo caan ah hman a si.
Cu bantuk thil sining cu nambat pakhat hi prime number a si le si lo kan check tikah a chuak tawn.

else block of a while loop

num = int(input('Enter an integer: '))
i = 2
while i <= num - 1 :
    if num % i == 0 :
        print(num, 'is not a prime number')
        break # Hika ah a break ahcun else block a tuah lai lo
    i += 1
else :
    print(num, 'is a prime number')

* else kan ṭialnak hmun (indentation) kha ṭha tein zoh. Hi else hi while loop ta a si, if statement ta a si lo.

A tanglei tahchunhnak ah hin else block cu a tuah lai lo, zeicatiah list chungah 3 a um. 3 cu 10 in hrawm khawh a si lo (non-multiple), cucaah 3 kan hmuh bak in loop kha kan hrawh (break) lai.

else block of a for loop

for ele in [10, 20, 30, 3, 40, 50] :
    if ele % 10 != 0 : 
        print(ele, 'is a not a multiple of 10')
        break
else : 
    print('all numbers in list are multiples of 10')

6.6 Nested Loops (Loop chungah loop dang)¶

Loop pakhat chungah loop dang kan hman chih khawh.
A leng loop (outer loop) voi khat a kal fatin, a chung loop (inner loop) kha a tling tein (a thawk in a dongh tiang) a kal dih lai.

nested loop

for i in range(1, 5) : # Outer loop
    for j in range(1, 5) : # Inner loop
        print(i, j)

Problems¶

Problem 6.1¶

p, n, le r value set 3 la law, set pakhat cio caah simple interest tuaknak program ṭial.

Program

Problem 6.1

i = 1
while i <= 3 : 
    p = float(input('Enter value of p: '))
    n = int(input('Enter value of n: '))
    r = float(input('Enter value of r: '))
    si = p * n * r / 100
    print('Simple interest = Rs. ' + str (si))
    i = i + 1

Output

Enter value of p: 1000
Enter value of n: 3
Enter value of r: 15.5
Simple interest = Rs. 465.0
Enter value of p: 2000
Enter value of n: 5
Enter value of r: 16.5
Simple interest = Rs. 1650.0
Enter value of p: 3000
Enter value of n: 2
Enter value of r: 10.45
Simple interest = Rs. 626.9999999999999

Problem 6.2¶

Infinite loop hman in nambat 1 in 10 tiang chuahnak (print) program ṭial. Nambat vialte kha tlar khat (same line) ah an chuak dih lai.

Program

Problem 6.2

i = 1 
while 1 : 
    print(i, end = ' ') 
    i += 1 
    if i > 10 : 
        break

Output

1 2 3 4 5 6 7 8 9 10

Tips

while 1 nih infinite loop a ser, zeicatiah 1 cu 'zero' a si lo, cucaah 'true' in a hmuh.
1 hmun ah nambat dang (zero a si lomi paoh) na hman ahcun infinite loop a ser thiamthiam lai.
Infinite loop sernak lam dang cu while True hman hi a si.
print() chung i end = ' ' nih khan iteration pakhat a kal fatin i a chuah (print) hnu ah 'space' a chiah. A sawhsawh (default) in cun end hi newline ('\n') a si.

Problem 6.3¶

Nambat 1, 2 le 3 hman in an i lo lomi (unique) combinations vialte chuahnak program ṭial.

Program

Problem 6.3

i = 1 
while i <= 3 : 
    j = 1 
    while j <= 3 : 
        k = 1
        while k <= 3 : 
            # An i lawh ahcun tuah lo in kal (skip)
            if i == j or j == k or k == i : 
                k += 1 
                continue 
            else :
                print(i, j, k)
            k += 1 
        j += 1
    i += 1

Output

Problem 6.4¶

Binary numeric string (nambat '0' le '1' lawng ummi) pakhat la law, cu nambat i a decimal value (kan hman tawnmi nambat) kawlnak program ṭial. Tahchunhnak ah, '1111' i a decimal value cu 15 a si.

Program

Problem 6.4

b = '1111'
i = 0 
while b : 
    # Current value kha 2 in karh law, binary digit (0 or 1) kha bet
    i = i * 2 + (ord(b[0]) - ord('0')) 
    # A hmasa bik digit kha hlonh law a tangmi laak
    b = b[1:]
print('Decimal value = ' + str(i))

Output

Decimal value = 15

Tips

ord('1') cu 49 a si, ord('0') cu 48 a si. (Cucaah ord('1') - ord('0') kan tuah tikah 1 a chuak, ord('0') - ord('0') tikah 0 a chuak).
b = b[1:] nih b string chung i a hmasa bik cafang kha a hlonh (strip).

Problem 6.5¶

for loop hman in a tanglei bantuk cafang pawl chuahnak (output) program ṭial: A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z, z,y,x,w,v,u,t,s,r,q,p,o,n,m,l,k,j,i,h,g,f,e,d,c,b,a,

Program

Problem 6.5

# A - Z tiang chuahnak
for alpha in range(65, 91) :
    print(chr(alpha), end=',')

print( ) # Tlar thar (New line) ah a thlen

# z - a tiang letthlit in chuahnak
for alpha in range(122, 96, -1) :
    print(chr(alpha), end=',')

Output

Problem 6.5

A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,
z,y,x,w,v,u,t,s,r,q,p,o,n,m,l,k,j,i,h,g,f,e,d,c,b,a,

Tips

Cafang A-Z i an Unicode value (nambat) cu 65 in 90 an si. Cafang a-z i an Unicode value cu 97 in 122 an si.
Print statement in a chuakmi paoh a donghnak ah comma (,) a tel lai.
A chungah zeihmanh a um lomi print( ) statement nih cursor kha tlar thar (next line) a thawknak ah a chiah.

Exercise¶

[A] Answer the following questions (A tanglei biahalnak pawl hi phi):¶

a. When does the else block of a while loop go to work? (while loop i else block kha zeitik ah dah a tuah?)

Phi: while loop i else block cu loop condition kha a pang tein a False tikah (loop a dih tikah) tuah a si. Asinain, loop kha break statement hman in kan hrawh (terminate) ahcun else block cu a tuah lai lo.

b. Can range( ) function be used to generate numbers from 0.1 to 1.0 in steps of 0.1? (range() function hi 0.1 in 1.0 tiang, 0.1 in karh nakhnga hman khawh a si maw?)

Phi: A ngah lo. Python ah range() function cu Integer (nambat tling) lawng caah hman khawh a si. Point nambat (float) caah cun numpy bantuk library hman a hau.

c. Can a while loop be nested within a for loop and vice versa? (while loop chungah for loop chiah a ngah maw, asiloah a let in a ngah maw?)

Phi: A ngah. Loop pakhat chungah loop phun dang chiah (Nested) hi a ngah.

d. Can a while/for loop be used in an if/else and vice versa? (if/else chungah loop hman a ngah maw, asiloah loop chungah if/else hman a ngah maw?)

Phi: A ngah. Control instruction pawl (loop, if-else) cu duh paoh in chawh in hman (nest) khawh an si.

e. Can a do-while loop be used to repeat a set of statements? (Statement pawl tuah ṭhan lengmang nakhnga do-while loop hman khawh a si maw?)

Phi: A ngah lo. Python language ah do-while loop a um lo.

f. How will you write an equivalent for loop for the following: (A tanglei while loop he a i tlukmi for loop zeitindah na ṭial lai?)

count = 1 
while count <= 10 :
    print(count)
    count = count + 1

* Phi: range() function hman a hau. 10 tiang a kal nakhnga stop value ah 11 kan chiah a hau.

(g) What will be the output of the following code snippet? (A tanglei code snippet nih zei output dah a chuah lai?)

for index in range(20, 10, -3) :
    print(index, end = ' ')

* Phi: 20 17 14 11

(h) Why should break and continue be always used with an if embedded in a while or for loop? (Zeicah break le continue hi while asiloah for loop chungah if he (condition he) hman a herh zungzal?)

Phi: if (condition) tel lo in break asiloah continue kan hman ahcun, loop a kal hmasa bik (first iteration) ah a tawp colh lai (break) asiloah a hlut colh lai (continue).
Cu tikah, loop chung i statement dang pawl kha zeitik hmanh ah a tuah kho ti lai lo (Unreachable code an si lai).
Cucaah, thil sining (condition) pakhatkhat a tlin lawngah loop hrawh/hlut kan duh tawn caah if he hman a herh.

[B] Point out the errors, if any, in the following programs:¶

(A tanglei program pawl ah hin a palhmi an um ahcun kawl/chim:)

a.

j = 1 
while j <= 10 :
    print(j)
    j++

b.

while true :
    print('Infinite loop')

c.

lst = [10, 20, 30, 40, 50]
for count = 1 to 5 :
    print(lst[ i ])

d.

i = 15
not while i < 10 :
    print(i)
    i -= 1

e.

# Print alphabets from A to Z
for alpha in range(65, 91) :
    print(ord(alpha), end=' ')

f.

for i in range(0.1, 1.0, 0.25) :
    print(i)

g.

i = 1
while i <= 10 :
    j = 1
    while j <= 5 :
        print(i, j )
        j += 1
    break
    print(i, j)
i += 1

[C] Match the following for the values each range( ) function will generate¶

(A tanglei range() function cio nih a chuah dingmi value (nambat tlar) pawl hi, a hmanmi he pehtlaih hna.)

a. range(5) 1. 1, 2, 3, 4
b. range(1, 10, 3) 2. 0, 1, 2, 3, 4
c. range(10, 1, -2) 3. Nothing
d. range(1, 5) 4. 10, 8, 6, 4, 2
e. range(-2) 5. 1, 4, 7

[D] Attempt the following questions:¶

(A tanglei biahalnak pawl hi phi i zuam:)

a. Write a program to print first 25 odd numbers using range( ). (range() function hman in odd number (nambat cawh) a hmasa bik 25 chuahnak program ṭial.)

b. Rewrite the following program using for loop. (for loop hman in a tanglei program hi ṭial ṭhan.)

Problem 6.6

lst = ['desert', 'dessert', 'to', 'too', 'lose', 'loose'] 
s = 'Mumbai'
i = 0
while i < len(lst) :
    if i > 3 :
        break
    else :
        print(i, lst[i], s[i])
    i += 1

c. Write a program to count the number of alphabets and number of digits in the string 'Nagpur-440010' (String 'Nagpur-440010' chungah cafang (alphabets) zeizat dah an um, cun nambat (digits) zeizat dah an um ti relnak program ṭial.)

d. A five-digit number is entered through the keyboard. Write a program to obtain the reversed number and to determine whether the original and reversed numbers are equal or not. (Keyboard in digit-5 ummi nambat ṭial a si. Cu nambat cu letthlit (reverse) in tuahnak le, a letthlit kan tuahmi le a hramthawk nambat kha an i luk maw luk lo ti check-nak program ṭial.)

e. Write a program to find the factorial value of any number entered through the keyboard. (Keyboard in ṭialmi nambat paoh i a 'factorial value' kawlnak program ṭial.)

f. Write a program to print out all Armstrong numbers between 1 and 500. If sum of cubes of each digit of the number is equal to the number itself, then the number is called an Armstrong number. For example, 153 = ( 1 * 1 * 1 ) + ( 5 * 5 * 5 ) + ( 3 * 3 * 3 ). (1 le 500 kar ah a ummi Armstrong number vialte chuahnak program ṭial. Nambat pakhat i a digit paoh kha voi 3 karh (cube) in kan fonh (sum) tikah, a hramthawk nambat he an i luk ahcun, cu nambat cu Armstrong number ti a si. Tahchunhnak: 153 = ( 1 * 1 * 1 ) + ( 5 * 5 * 5 ) + ( 3 * 3 * 3 ).)

g. Write a program to print all prime numbers from 1 to 300. (1 in 300 kar ah a ummi prime number vialte chuahnak program ṭial.)

h. Write a program to print the multiplication table of the number entered by the user. The table should get displayed in the following form: (User nih a ṭialmi nambat i a a-li (multiplication table) chuahnak program ṭial. Table cu a tanglei bantuk in langhter ding:)

29 * 1 = 29
29 * 2 = 58
...

i. When interest compounds q times per year at an annual rate of r % for n years, the principal p compounds to an amount a as per the following formula: \(a = p ( 1 + \frac{r}{q} )^{nq}\) Write a program to read 10 sets of p, r, n & q and calculate the corresponding as. (Kum khat ah q voi a karh (compound) mi interest r% in kum n chung a um tikah, a hram p cu a tanglei formula ning in a ah a cang: \(a = p ( 1 + \frac{r}{q} )^{nq}\). p, r, n le q set 10 la law, a chuakmi a tuaknak program ṭial.)

j. Write a program to generate all Pythagorean Triplets with side length less than or equal to 30. (Sir (side) pakhat cio 30 nak in a tlawm deuh asiloah a tlukmi Pythagorean Triplets vialte chuahnak program ṭial.)

k. Population of a town today is 100000. The population has increased steadily at the rate of 10 % per year for last 10 years. Write a program to determine the population at the end of each year in the last decade. (Tuchun ah khua pakhat i milu cu 100,000 an si. A luan ciami kum 10 chung khan, kum khat ah 10% in hma a panh (karh) lengmang. A luan ciami kum 10 chung i kum khat a dih fatin milu zeizat dah an si ti kawlnak program ṭial.)

l. Ramanujan number is the smallest number that can be expressed as sum of two cubes in two different ways. Write a program to print all such numbers up to a reasonable limit. (Ramanujan number timi cu nambat pahnih i an cube (voi thum karh) fonh in, lam phun hnih in hmuh khawhmi nambat hme bik a si. Cu bantuk nambat pawl cu a niamnak tawk (reasonable limit) tiang chuahnak program ṭial.)

m. Write a program to print 24 hours of day with suitable suffixes like AM, PM, Noon and Midnight. (Nikhat chung suimilam 24 kha AM, PM, Noon le Midnight tiah a hmanmi ṭhiam in chuahnak program ṭial.)

Chapter 6 Repetition Control Instructions¶

Repetition Control Instructions

Keynote¶

6.1 Repetition Control Instructions (Zei dah an si?)¶

1. The while Loop¶

6.2 While loop hman ning¶

6.3 For loop hman ning¶

6.4 break le continue¶

6.5 Loop i Else Block¶

6.6 Nested Loops (Loop chungah loop dang)¶

Problems¶

Problem 6.1¶

Problem 6.2¶

Problem 6.2¶

Problem 6.3¶

Problem 6.4¶

Problem 6.5¶

Exercise¶

[A] Answer the following questions (A tanglei biahalnak pawl hi phi):¶

[B] Point out the errors, if any, in the following programs:¶

[C] Match the following for the values each range( ) function will generate¶

[D] Attempt the following questions:¶

Comments

1. The `while` Loop¶