Done by: Esonboyev Umid python 3 -bsic operators, Decision making (if),Nested If Statements

Done by: Esonboyev Umid

• PYTHON 3 –Bsic operators, Decision making (if),Nested If Statements.

Logical AND and Nesting

• If we have the && operator, do we need nesting?

if(BooleanExpression1) {

if(BooleanExpression2) {

Both conditions met

}

else {

Both conditions NOT met

}

}

else {

Both conditions NOT met

}

if(BooleanExpression1 && BooleanExpression2) {

Both conditions met

}

else {

Both conditions NOT met

}

Logical AND and Nesting

• Answer: Yes, to act if one of the conditions is not met:

if(BooleanExpression1) {

if(BooleanExpression2) {

Both conditions met

}

else {

Condition 2 not met

}

}

else {

Condition 1 not met

}

if(BooleanExpression1 && BooleanExpression2) {

Both conditions met

}

else {

Both conditions NOT met

}

Exercise

• Change NestedIfStatement.java to tell the user if she does not meet one requirement, the other requirement, or BOTH.
• Hint: we talked about something last lecture that will help us…
• Flags

Logical OR Example

• New Topics:
• Logical OR

Exercise

• Change LogicalOrOperator.java to allow the user to enter capital or lower case Y or N as an answer.
• Hint
• Use another OR operator.
• Also, check to make sure the user entered a valid response.
• Y, N, y, or n.

Comparing String Objects

• Imagine you have declared two String variables as such:

String x = "buffalo";

String y = “bison";

• What does x == y resolve to?
• false, but not for the reason you think!
• The == operator compares what the reference values are (what objects they are pointing to), NOT what the value of the string is.
• In some cases this causes problems
• You should use methods in the String class in order to compare String variables
• equals
• compareTo

String equals method

• To check if two strings are the same you can use the equals method.

StringReference.equals(OtherString);

• If the string referred to by StringReference is equal to the one referred to by OtherString, then true is returned.
• Otherwise false is returned.
• This comparison is case-sensitive ("buffalo" and "Buffalo" are not equal)
• To do case-insensitive comparison, use equalsIgnoreCase

String compareTo method

• If you want to determine which string is “greater” use the compareTo method.

StringReference.compareTo(OtherString);

• If the string referred to by StringReference is equal to the one referred to by OtherString, then 0 is returned.
• If the string referred to by StringReference is “less than” to the one referred to by OtherString, then a negative number is is returned.
• If the string referred to by StringReference is “greater than” to the one referred to by OtherString , then a positive number is returned.
• This comparison is case-sensitive ("buffalo" and "Buffalo" are not equal)
• To do case-insensitive comparison, use compareToIgnoreCase

String compareTo method

• What does it mean for strings to be “greater than” or “less than” each other?
• Java compares the two strings, character by character from left to right.
• When there is a difference in a character it compares the Unicode values of the characters.
• If a string is shorter than another, and the shorter one is the beginning of the longer one, the shorter one is considered less.
• "hi" is less than "high"

String Comparison Example

• New Topics:
• String == operator
• equals method
• compareTo method

Block-Level Scope

• If a variable is declared inside of a block, it is said to have block-level scope.
• If a variable has Block-Level Scope it is in scope from its declaration to the ending of the block in which it was declared.

if(BooleanExpression) {

int x;

…

}

• The variable x has scope from the point it was declared to the }
• This does not have much use now, but will be more useful when we learn loops.

The Conditional Operator

• Java provides and operator to create short expressions that work like if-else statements.

BooleanExpression ? Value1 : Value2;

• If BooleanExpression is true, Value1 is returned
• If BooleanExpression is false, Value2 is returned
• Example:

if (score < 60)

System.out.println("You Fail");

else

System.out.println("You Pass");

System.out.println("You "

+ score < 60 ? "Fail" : "Pass");