Page 277 - Computer Science V2.0 Class 11

The above flow diagram translates into the following syntax description:

if <conditional expression>: ……………………………..header
<sequence of statement(s)> ………………...if suite/block
elif <conditional expression 1>:
<sequence of statement(s)> ………………...elif suite/block 1
elif <conditional expression 2>:
<sequence of statement(s)> ………………...elif suite/block 2

elif <conditional expression 3>:
<sequence of statement(s)> ………………...elif suite/block 3
….

elif <conditional expression n>:
<sequence of statement(s)> ………………...elif suite/block n
[else:
<sequence of statement(s)>] ………optional else suite/block
The above description can be made more concise as follows:

if <conditional expression>:
<sequence of statement(s)> …………..if suite/block
[elif <conditional expression 1>: ……………………optional elif part
<sequence of statement(s)>…] ……………elif suite/block
[else:
<sequence of statement(s)>] ……… optional else suite/block
As the above syntax suggests, several conditional expressions involving multiple header clauses can be tested
one by one using an if-elif-else statement. If the conditional expression specified in the if header yields
(on evaluation) True, the sequence of statements in the if block is executed, and the rest of the if-elif-else

statement is ignored by the Python interpreter. In the other case, when the conditional expression specified in the if
header yields (on evaluation) False but the conditional expression specified in some of the elif headers yields
(on evaluation) True, then the sequence of statements in the first elif block for which its conditional expression
yields (on evaluation) True will be executed, and the rest of the if-elif-else statement will be ignored by the
Python interpreter. One can specify as many elif clauses as required in an if-elif-else statement. When the
conditional expression specified in the if header, as well as each of the elif headers, yields (on evaluation) False,
the sequence of the statements in the else block will be executed. However, it is not mandatory to include an else
clause. All the statements in a block are indented at the same level. As mentioned above, as soon as the conditional
expression in a header yields True, the sequence of statements in its block is executed, and control moves to the
statement immediately following the if-elif-else/ if-elif statement.
Next, let us rewrite Program 10.5, making use of the elif clause.

Program 10.6 Write a function grade(percentage) that computes the student's grade based on the student's
percentage and the cut-off marks specified for that grade using elif clause.

percentage grade
>=75 A
>=60 B
>=50 C
>=33 D
< 33 F

Conditional Statements 263