Flow Control
In which order, statements are going to execute, is decided by flow control.
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Types of flow control statement:
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Conditional statements/Selection Statements (if, if-else, if-elif-else)
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Iterative Statements (loops for and while)
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Transfer Statements (break, continue, pass)
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Now I am going to discuss these 3 types of flow control statements in detail.
Conditional Statements/Selection Statements:
Among multiple available options select one and execute it, such type of statements are considered as Conditional or Selection statements. Various Conditional statements are:
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if
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if-else
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if-elif-else
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if syntax:
if condition:
statements
Example:
in the above example if the name equals to ‘mujtaba’ then the corresponding If condition is executed.
If-else syntax::
if condition:
statements
else condition:
statements
Example:
If-elif-else syntax:
if condition:
statements
elif condition:
statements
else condition:
statements
Example:
Note 1: We can take any number of elif conditions after if condition.
Note 2: else is always optional.
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Possible combinations of if:
If
If else
If elif else
If elif
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Some programs on conditional statements:
#Program to find biggest of given 2 numbers from the keyboard
#Program to find biggest of given 3 numbers from the keyboard
Note: In this example we are using eval function so that number can be any type int or float.
#Write a program to check whether the given number is even or odd
Iterative Statements (loops for and while):
Some times we require a group of statement execute iteratively until the given condition is true.
for loop: also known as for-each loop
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Syntax:
For each_element in sequence:
do some action
Sequence can be string, list, range tuple or set.
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Example:
Example: Enter a string from keyboard and count number of characters in string.
Example: Print numbers from 0 to 10
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for loop
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while (in python there is no do while loop)
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Example: Print numbers from 10 to 1 in descending order.
Example: Print sum of numbers of list.
Note: for loop is mostly recommended in python. If we don't know the number of Iteration in advance then while loop is used.
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While Loop syntax:
while condition:
body
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Example: Print numbers from 1 to 10 using while loop.
Example: Sum of first n numbers
When to use ‘for loop’ and ‘while loop’?
If the number of iterations are known in advance, ‘for loop’ will be used otherwise 'while loop' will be used.
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Nested Loops:
loop inside a loop is known as Nested loops.
Ex: print the below pattern.
*
* *
* * *
* * * *
* * * * *
Example: Print the below pattern.
1
2 2
3 3 3
4 4 4 4
Transfer Statements:
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break
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continue
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pass
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break: ‘break’ is used to break loop execution based on some condition.
Example:
continue: We can use continue within loop to skip the current iteration and go to the next iteration
Example: Print all odd numbers up to 10 by using continue.
pass: pass is a keyword in python. In our programming syntactically if block is required, which won’t do anything, then we can use pass. It is an empty/null statement like other languages.
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Example:
