More on Assignment and Console Input

1
More on Assignment and Console Input

• Overview
• Increment Decrement Operators
• Short-cut Operators
• Casting
• Math class
• Console Input (TextIO class)
• Preview Control Structures

2
Increment or Decrement Operators

• Increment/decrement operations (count count
  1) are very common in programming. Java
  provides operators that make these operations
  shorter.
• Operator Use Description
• op Increments op by 1
• evaluates to a value before
  incrementing
• op Increments op by 1
• evaluates to a value after
  incrementing
• -- op-- Decrements op by 1
• evaluates to a value before
  decrementing
• -- --op Decrements op by 1
• evaluates to a value after
  decrementing

3
Increment or Decrement Operators

• Example
• 1. What is the value of j and i after executing
  the following code?
• i 1
• j 5
• j i
• 2. What is the value of j and i after executing
  the following code?
• i 10
• j 50
• j i--
• 3. What is the value of j and i after executing
  the following code?
• i 5
• j 10
• i
• j

4
Short Hand Operators

• Java also provides a number of operators that
  can be used as a short-cut for performing
  arithmetic operations on a variable and assigning
  the result to the same variable.
• Operator Short-Form Equivalent to
• op1 op2 op1 op1 op2
• - op1 - op2 op1 op1 - op2
• op1 op2 op1 op1 op2
• / op1 / op2 op1 op1 / op2
• op1 op2 op1 op1 op2
• Example
• Instead of writing
• a a 5
• We can write
• a 5
• If the variable name on both sides of assignment
  operator are same then bring the operator ,
  before the operator.
• a a 5

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Casting

• We learnt earlier that the following division
• 5 / 2
• results in 2
• Because the / operator is operating between 2
  integer type constants and so the result will be
  an integer.
• To get 2.5 , we need to convert either 1 or both
  the operands to double . Then the division will
  look like
• 5.0 / 2.0
• But what if we have integer variables to divide
  each other, like a / b ?
• For this, cast operator is used .
• (double) a / (double) b

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Primitive Casting

• Conversion of primitives is accomplished by (1)
  assignment and/or (2) explicit casting
• int total 100
• float temp total // temp now holds
  100.0
• When changing type that will result in a loss of
  precision, an explicit cast is needed. This is
  done by placing the new type in parenthesis
• float total 100F
• int temp total // ERROR!
• int start (int) total

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Methods in java.lang.Math

Method Argument type(s) Functionality
Math.abs(a) Int/ long/ float/ double Absolute value
Math.ceil (a) Double Smallest whole number greater than or equal to a
Math.cos(a) Double Cosine
Math.exp(a) Double Exponential number to the power of a
Math.floor(a) Double Largest whole number less than or equal to a
Math.log(a) Double Natural logarithm of a
Math.max(a, b) Int/ long/ float/ double Maximum
Math.min(a, b) Int/ long/ floa / double Minimum
Math.pow(a, b) Double a to the power of b
Math.random() None Random number generator
Math.rint(a) Double Converts double value to integral value in double format
Math.round(a) Double Rounds into closest long
Math.sin(a) Double Sine
Math.sqrt(a) Double Square root
Math.tan(a) Double Tangent
 
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Console Input

• Reading input from the console (text mode) is a
  bit complex for beginners to Java.
• To avoid this complexity, we shall initially be
  using a class, TextIO, which has been designed to
  simplify console input operations.
• The TextIO class has the following methods which
  are used to read the desired type of input.
• readByte() reads a byte from the data
  source.
• readChar() reads a character.
• readDouble() reads a double
• readFloat() reads a floate.
• readInt() reads an integer.
• readLong() reads a long integer.
• readShort() reads a short integer.
• readString() reads a string made out of
  non-white
• space

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Console Input

• To use the TextIO class, you need to add the
  following pieces of code to your programs
• Import the TextIO class by placing the following
  import statement at the beginning of your
  program
• import TextIO
• Create a TextIO object as a field inside your
  class
• static TextIO stdin new
• TextIO(System.in)
• Note The parmeter to TextIO can be keyboard
  (System.in), a data file or a URL
• Change the heading of the main method as follows
• public static void main(String args)
  throws java.io.IOException
• For all these to work, you need to copy the file
  TextIO.class to the same folder containing your
  program.
• You can get the TextIO.class as well as its
  source (.java) on the following URL
• http//www.ccse.kfupm.edu.sa/bmghandi/001/utils.
  html

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Evaluating Expressions Arithmetic Expression
Example

• import TextIO
• class Expressions
• static TextIO stdin new
• TextIO(System.in)
• public static void main(Stringargs) throws
  java.io.IOException
• double e
• int a, b, c
• a stdin.readInt()
• b stdin.readInt()
• c stdin.readInt()
• e a b c
• System.out.println("abc " e)

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Evaluating Arithmetic Expression With Simple
Math functions - Example

• import TextIO
• class Expressions
• static TextIO stdin new TextIO(System.in)
• public static void main(Stringargs)
• throws java.io.IOException
• double a,c
• int r
• r stdin.readInt()
• a Math.PI Math.pow(r,2)
• c 2 Math.PI r
• System.out.println("Area " a)
• System.out.println("Circum. " c)