Conditional or Decision Making Statement

Program that causes a jump of control from one block to the other is called conditional statements.

There are four types:

• if
• if…else
• if…elif…else
• nested if

if statement

If the test expression is true then the statement block or “body of if” will be executed.

Syntax:

if text expression:

    statement (s) or body of if

Flow chart:

Example

A = 20

B = 30

if A<B:

    print(“A is less than B”)

Output

A is less than B

if…else statement

If the test expression is true then “body of if” will be executed. Otherwise if the test expression is false then “body of else” will be excecuted

Syntax:

if text expression:

    body of if

else:

    body of else

Flow chart:

Example

A = 20

B = 30

if A<B:

    print(“A is less than B”)

else:

    print(“A is not less than B”)

Output

A is less than B

if…elif…else statement

If there are more than two possibilities then we need more than two branches. Each condition is checked in order. If the first condition is false then the next condition is checked and son on. If anyone of the condition is true then the corresponding branch will be executed

Syntax:

if text expression:

    body of if

elif test expressin:

    body of elif

elif test expressin:

    body of elif

else:

    body of else

Flow chart:

Example

A = 20

B = 30

if A!=B:

    print(“A is not equal to B”)

elif A<B:

    print(“A is less than B”)

else:

    print(“A is not less than B”)

Output

A is not equal to B

Nested if statement

If statement within the another if statement is called nested if statement

Syntax:

if text expression:

    body of if

    if test expressin:

        body of if

    else:

        body of else

else:

    body of else

Flow chart:

Example

A = 20

B = 30

if A!=B:

    print(“A is not equal to B”)

    if A<B:

        print(“A is less than B”)

    else:

        print(“A is not less than B”)

else:

    print(“A is equal to B”)

Output

A is not equal to B

A is less than B