Programming -1
If…. else and Switch
statements
Objective
In this chapter you’ll:
• The concept of decision making in programming and logical operations.
• Concept of process control and conditional statements.
• Logical operations coefficients
• Conditional test statement if
• Conditional test statement if… Else
• Conditional test statement if Else if
• Conditional test statement nested if
• Conditional test statement Switch
Decision making
Decision making
• If you want to get to college and encounter an intersection ,You should now make a logical decision to answer the following questions
• Will you turn right will reach you to college?
• Will you turn left will reach you to college?
• If you continue to the front , will you reach the college?
• All of these questions can answer yes or no to determine the right path
• in Java and the yes/ no value is true / false (Boolean data type ) to make appropriate decisions.
Process control
in real life..
❖ Determine the success of a student in a course - Is the total greater than or equal to 60 marks. ( Yes / No)
❖ Speed violation - Is the speed greater than the specified speed
e.g. 120 m / s. (Yes / No)
In Java ..
These controls and conditions need to be checked using comparisons (logical operations) whose results are logical (ie yes, no).
Logical Operations
Logical operations are those processes that are mainly used in decision-making, e.g. these determine they must be walk in one direction and leave another.
Types of logical operations:
• Simple operations (one condition).
• Combined operations (two conditions or more).
Simple logical operations
• ==
• !=
• >
• <
• >=
• <=
Complex logical operations• Complex logical operations consist of more than one of a simple comparison process
that is combined using the following operations
UsingOperations
When we need to link the processes to both simple comparisons are
correct (And)
&&
When we need to link the processes at least one
of the two simple operations are correct (OR).
||
When we need to reverse the value of comparisons, it means NOT and is
used with one simple comparison
!
Truth tables for complex logical operations
An example of logical operations
Note: We use ( = )to specify a value while we use(==) to compare and return a boolean value
Boolean datatype
Define
Boolean
variables
Assign
value
Print Boolean
variabels
Boolean datatype
Boolean datatype
• if value1 and value2 have the same values the result is true, if not the result is false.
Compare variables
Compare variables
Why ??
Compare variables
we need to compare text values rather than memory locations as they are not basic data types
Compare variables
Use equals() for compare string variables
Concept of operations in programming
• The execution of any task in our life consists of a series of sometimes sequentialand sometimes parallel processes.
• In the world of programming, there is a method followed by the compiler in theimplementation of the code and is to follow the code and the execution ofcommands in the order set by the programmer.
• Did you notice that the translator outputs the results by walking with thesentences of the program one by one, did not provide one over the other and didnot repeat one of them more than times exist, and did not ignore any of them ?!
• This is called the sequential process, but !!
• When a programmer forces a compiler to execute strings and leave strings, orexecute sentences more than their appearance, this is known as controlling theflow of operations.
Conditional sentences• Conditional sentences are statements that help to choice of two or more things.
• E.g. She says if the IT specialty has a good field of work I will specialize in it or I will search for another specialty.
• The selection sentences have more than one pattern, as in the following table:
UsingConditional
sentences
interested in one way on one conditionIf
interested in two different ways on one conditionIf ..else
interested in more than two different ways more than one conditionIf ..else if
interested in more than two overlapping roads with more than one
condition
Nested if
When multiple conditions exist, they only have to do with specific valuesSwitch
Selection sentences
Consists of three parts:
• 1- Decision making statements (IF, IF .. Else,....)
• 2- Condition (logical operations).
• 3 –statments (Executing orders) as a result of whether or not the condition is done.
Enter value condition
statements with true
True
False
statements with false
IF statement
• If (condition )
One process;
• If (condition )
{
multi process;
}
How to write:
• The value of condition is Boolean
IF statement
IF statement example:
What is the output???
Second if statement
IF statement
When the condition is related to the execution of more
than one sentence, we put these sentences between
the brackets and this makes the translator executes
them together if the condition meets.
Common error
• Common error: The condition variable does not contain a value that causes the compiler to show a Syntax error when executed.
• Common error: Placing the semicolon immediately after the condition statement shows a logical error (it appears only through the search and test process after execution), because the translator understands this comma as the condition is unanswered and therefore performs the following sentences without restrictions.
IF…Else
• If (condition )
One process;
Else
Another process;
• If (condition )
{
multi process;
}
Else
{
another multi process;
}
How to write:
• The value of condition is Boolean
IF…Else example
IF…Else example
IF…Else
• Two if statements can be replaced with if ... else
• if .. else better because it is do only one comparison
Common error• Common error: Placing the semicolon immediately after the else statement shows a logical
error, because the interpreter understands this comma as an exception and therefore performs the following statements without restriction.
• If the answer in the if else clause contains more than one command, they must be enclosed in the brackets of the beginning and the end, otherwise it will show a programmatic error because it will be considered that the condition is expired and else remains without if.
This statment will be executed in this way anyway though
not intended by the programmer
IF….Else if
• Repeated depend of the number of conditions
• If ( first-condition )
{
multi process;
}
Elseif ( second-condition )
{
second multi process;
}
Else
{
Third multi process;
}
IF….Else if
• Note in the if… else if all conditions are contradictory and each condition cannot be met with another condition being met.
• Common error: If you want to check the equality of two numbers, use the = sign or use == with a space between them.
• Common error: The separation of the>< sign and the = sign is considered a error.
Can the If statements be nested?
• in java the if statement may be inside another if statement
Can the If statements nested?
nested if example
Switch statement
• It depends on the existence of alternatives equal to the value being tested and through which we can choose between alternatives, write as follows:
Switch statement
• Switch statement use the following resaved word:
• switch determine the variable
• case comparison the value of switch variable
• default it is option execute when no match with case value
• break it is the last statement in each case list, word to control process in the end of switch statement
break
Switch statement
day =4
????
day =6
????
IF and Switch Comparison
1. switch simple than if statement
2. switch easy to read and understand the details
3. switch can use with conditions have == sing
4. better performance
switch Fall Through
• If no break in case statement.
switch Fall Through
• If no break in case statement.
Summary
• The concept of decision making in programming and logical operations.
• Concept of process control and conditional statements.
• Logical operations coefficients
• Conditional test statement if
• Conditional test statement if… Else
• Conditional test statement if Else if
• Conditional test statement nested if
• Conditional test statement Switch
