Standard Input and Output

1
Standard Input and Output
2
To OUTPUT you require

• include ltstdio.hgt
• printf(format string, data list)
• Field specifiers are inside the format string
• i.e. Controls how the data looks when printed

3
Standard printf statements
include ltstdio.hgt void main( ) / This codes
prints the values of two variables / int a
57 int b 145 printf( "d\nd\n",
a,b) return
4
What happened?

• The statements
• int a 57 a 57
• int b 145 b 145

The statement printf( "d\nd\n", a , b) prints
57 145
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Field Specifiers

• ltflaggtltminimum widthgtltprecisiongtltsizegtcode
• Codes

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Specification of Width
7

• Precision specification for floats
• 7.2f
• / this prints the float in a field of seven
  characters with two characters after decimal
• nnnn.dd /

8
Another Example of printf

• include ltstdio.hgt
• int main()
• / This codes prints the values of two variables
  /
• int months 9
• double salary 145.35
• printf( "d\n7.2f\n", months , salary)
• return 0

9
The output

• 9
• 145.35

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Another Example of printf

• include ltstdio.hgt
• int main( )
• / This codes prints the values of two variables
  /
• int months 9
• double salary 145.35
• printf( "the number of months is4d\nthe
  salary is7.2f\n", months,salary)
• return 0

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The output
the number of months is 9 the salary is 145.35
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Input Getting information into memory input
(or reading)

• Requires
• include ltstdio.hgt
• scanf(format string, address list)
• Again Field specifiers inside the format string

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Standard scanf Statements

• scanf(format string, address list)
• scanf(df, age, weight)
• At keyboard type 23 60.75
• Result weight
• age

60.75
23
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Field Specifiers

• ltflaggtltmaximum widthgtltsizegtcode
• Remember There is no precision issue here !!!
• Codes

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Rules for scanf formats

• Addresses of a variable are specified with
• variableName
• A variety of rules apply to conversion

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Rules for scanf formats

• Initial whitespace is ignored (except c)
• The conversion operation process until
• End of file is reached
• Maximum characters are processed
• A whitespace character is found after a digit
• An error is detected

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Rules for scanf format strings

• A field specifier for each variable
• Other characters must be exactly matched
• Cannot end format string with whitespace

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Examples of scanf

• scanf(dddc,a,b,c,d)
• scanf(ddd c,a,b,c,d)
• scanf(-8d-8dd,a,b,c)
• -8d / left justify flag /

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Working with the variables

• We want to operate on variables e.g add two
  variables or subtract them.
• An Expression
• rateOfPayhours tax

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Operators

• e.g., plus
• - minus
• multiply
• / divide
• mod
• You create expressions out of operators.

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Some Expressions

• 35
• 2 3 4
• 23 b 6
• -salary
• Use parenthesis to clarify complicated
  expressions
• (food drinks)(1gstpst)

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Assignment

• Assignment expressions evaluate to the expression
  on the right of the assignment operator.

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Simple Assignment
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Operator Precedence

• Operators have a built in order of precedence
  which is over ridden by using parenthesis
• 1234 answer 11
• 12 35 answer 17
• -562 answer -28

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Operators precedence (on the same level they are
equal)

• 1. ( ) takes precedence
• 2. unary minus -7 unary plus 3
  
• 3. Multiply / Divide
  
• 4 Modulus
• 5. add - subtract

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Examples Operators

• Examples of C statements using these
• The following is a program fragment only
• int i, j ,k, l, m
• i j k
• i j k l / m
• / Here i gets the value j (kl/m) /
• i j k l m
• / Here i gets the value (jk) (lm) /

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Examples Operators

• Examples of C statements using these
• There is one division operator for integer and
  float but it means different things.
• 2 / 5 ? 0
• 2.0 / 5.0 ? 0.4
• is the modulus (remainder) operation
• 5 2 ? 1
• 2 5 ? 2

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Unary operator and -

• a evaluates to the contents of a
• -a evaluates to the negative contents of a

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Unary Expressions
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Unary operator and --

• Post-increment and decrement
• i i--
• /First use the value then do operation/
• Pre-increment and decrement
• i --i
• /First do operation then use the value /

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Unary operator and --

• Examples for int i , j , k
• i1
• i / i ? 2 /
• j i /j ? 2 and then i ? 3
• j i / i ? 4 and then j ? 4
• j i-- / j ? 4 and then i ? 3
• Note that i and ii1 are equivalent
• Note that i-- and ii-1 are equivalent

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Binary Compound Operators

• Often a variable is changed as follows
• i i 5 / Take the value of i add 5 and put
  the result back into the variable i/.
• Leads to new assignment operators
• - /
• i i 1 same as i 1
• j j k same as j k

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Compound Assignment
34
A Simple Program

• include ltstdio.hgt
• int main( void )
• double x, y,z
• printf("Pls. input two real numbers\n")
• scanf("ff",x,y)
• z x y
• printf("x6.2f y6.2f z 6.3f \n",x,y,z)
• return(0)

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A Simple Program

• The OUTPUT
• gtPlease input two real numbers
• 23.4 45.6
• x 23.40 y 45.60 z69.000

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• / A simple program to average 3 numbers/
• include ltstdio.hgt
• int main(void)
• float number1,number2,number3,sum,average
• printf("\n Please enter number1. ")
• scanf("f",number1)
• printf("\n Please enter number2. ")
• scanf("f",number2)
• printf("\n Please enter number3. ")
• scanf("f",number3)
• sum number1number2number3
• average sum/3.0
• printf("\nthe sum of f f and f is
  f",number1,
• number2,number3, sum)
• printf("\nthe average is f\n",average)
• return 0

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• Whats the problem with the previous program?
• What if you wanted to average 50 numbers?
• It would be very clumsy to repeat 50 times.
• Also you have to change the program each time
  you have a different number of numbers.

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Program to calculate tax on a bill

• First you have to know the facts.
• Subtotal food and drink
• PST 0.08
• GST 0.06
• Tax subtotal (PSTGST)
• Total subtotal tax

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• / A simple program calculate restaurant bill
  input food and drink amounts
• output subtotal, tax, total
  bill/
• include ltstdio.hgt
• define PST 0.08
• define GST 0.06
• int main(void)
• float food,drink,sum,total,tax
• printf("\n Please enter food total. ")
• scanf("f",food)
• printf("\n Please enter drink total. ")
• scanf("f",drink)
• sum food drink
• tax sum(GST PST)
• total sumtax
• printf("\nthe food total is 6.2f ",food)
• printf("\nthe drink total is 6.2f ",drink)
• printf("\n ")
• printf("\nthe subtotal is 6.2f ",sum)
• printf("\nthe tax is 6.2f ",tax)

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• Whats the problem with the previous program?
• The rule is not right. If the subtotal is less
  than 3.00 the no GST
• So we need decision possibility
• So we need CONTROL STRUCTURES

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Unary Operator sizeof

• sizeof is an operator. It is NOT a function
• Evaluates to number of bytes for that item
• sizeof(int)
• sizeof(x)
• sizeof(3.256)