3 Flow Control

Flow control describes the order in which statements will be executed at runtime.

Python has 3 types of control-flow

• Conditional Statements or Decision Making statements

if
if-else
if-elif-else

• Iterative Statements

for
while

• Transfer Statements

break
continue
pass

3.1 Conditional (Decision Making) statements

It is kind of making decision during occurred situation of program execution and action can be taken according to specified conditions.

Structure of decision making evaluate several expressions that provide True or False as a result.

It is up to you to decide which type of action want to take and execute the statements based upon True and False.

# if Statements
age=18
if age>=18:
    print("You are eligible to vote")

if-else statement have a block of code, where if is executed when it is 1 or True and else when if is 0 or False

# if-else satetements
n1, n2 = 2, 4
if n1>n2:
    print("if")
else:
    print("else")

The elif statement is used to check for the multiple True expressions and so on if the condition is True it execute a block of code.

# if-elif-else statement
n = 2
if n==0:
    print("if")
elif n==1:
    print("elif")
else:
    print('else')

Nested if-else statement is used to check condition inside another check condition

# Nested if-else statement
price = 33
if price > 30:
    if price > 100:
        print("if-if")
    else:
       print("if-else") 
elif price > 20:
    if price > 15:
        print("elif-if")
    else:
       print("elif-else") 
else:
    print("else")

3.2 Iterative Statements

In loop, the statements are sequentially executed, execution of first function statement is done first, then second and so on.

In situation where you need to perform a block of code many times then loop statement will come in to picture.

It allows to execute/run group of statements or a statement multiple time.

for loop

If we want to execute some action for every element present in some sequence(it may be string or collection)then we should go for for loop.

nlist = ['Amrit', 1, 2, 3, 4, 'apple', 'banana']
for x in nlist:
    print(x, end=', ')
# Amrit, 1, 2, 3, 4, apple, banana,

for i in range(1, 5):
    print(i, end=' ')
# 1 2 3 4

for i in range(0, 7, 2):
    print(i, end=' ')
# 0 2 4 6

# Nested Loops
for i in range(4):
    for j in range(4):
        print((i, j), end=', ')
    print()
# (0, 0), (0, 1), (0, 2), (0, 3), 
# (1, 0), (1, 1), (1, 2), (1, 3), 
# (2, 0), (2, 1), (2, 2), (2, 3), 
# (3, 0), (3, 1), (3, 2), (3, 3)

while loop

If we want to execute a group of statements iteratively until some condition false, then we should go for while loop.

total_amount=200
while total_amount > 0:
    print(total_amount)
    total_amount=total_amount-100
else:
    print("Put more money bank people")
    
# 200
# 100
# Put more money bank people

# Infinite Loops
i=0;
while True:
    i=i+1;
    print("Hello", i)

3.3 Transfer Statements

break

It is used for a premature terminates of current loop immediately and executes the further statement, just like break statement in C language.

for i in range(10):
    if i==7:
        print("processing is enough..plz break")
        break

# processing is enough..plz break

continue

We can use continue statement to skip current iteration ithout performing remaining statements in present iteration and continue next iteration.

for i in range(10):
    if i%2==0:
        continue
    print(i, end=' ')
# 1 3 5 7 9

pass

Used to define an empty block with pass keyword.

The pass statement is considered as a null statement which won't do anything. It is useful when a code (i.e., code required in future) has not written till now, but your code will go eventually.

def m1():
    pass


for i in range(20):
    if i%9==0:
        print(i, end=' ')
    else:
        pass
# 0 9 18