Topic 2: C Overview

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Topic 2 C Overview

• C Language Elements
• Variable Declaration and Data Types
• Statement Execution
• C Program Layout
• Formatting Output
• Interactive Mode, Batch Mode and Program
  Redirection

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C Language Elements Preprocessor Directives

• (sign for preprocessor directive commands)
• include ltstandard header filegt
• include ltstdio.hgt
• include ltmath.hgt
• Standard header file (.h)
• Library

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C Language Elements Preprocessor Directives

• Constant Macros
• Program does not change their values
• define Name value
• define KILOS_PER_POUND 0.45359
• define MILES_PER_KM 0.62137
• define PI 3.141593

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C Language Elements Function main

• Every C program has main function
• Main function has heading and body
• A function body has declarations and executable
  statements
• int
• main(void)
• printf("This is a C program\n")
• return (0)

The control returns back to OS
Program was executed without
error
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C Language Elements Reserved Words

• They have special meaning and can not be used for
  something else
• All are lowercase
• some of the reserved words are
• void case switch
• return for signed
• else long if
• do int while

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C Language Elements Identifiers

• Standard identifiers For example scanf or printf
  are the names of defined operations
• User-defined identifiers (should begin with a
  letter and only can contain digit or _ )
• Invalid Valid
• 1rate rate1
• int Rate1
• joes joe
• Uppercase lowercase User-defined identifiers
  are considered different identifiers by C
  compiler
• Meaningful name should be used for User-defined
  identifiers

Different identifiers
It is a reserved word
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C Language Elements Variable and data types

• Variables are the name (identifiers) for memory
  cells that can be changed
• It should start with a data type
• int count
• double x,y,z
• char first_initial

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C Language Elements Data types

• int integer between -32767 to 32767
• double for real numbers
• 3.14, 0.34
• 1.23e5, 1.23E5 1.23 10 to the power 5
• 0.34e-4 0.000034
• char for showing individual character
• A, a, ,...

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• / Convert the weight from pounds to kilograms /
  comment
• include ltstdio.hgt standard header file
  preprocessor
• define KILOS_PER_POUND 0.45359 constant macro
  directive
• int reserved word
• main(void)
• double pounds, variable
• kilos
• printf(" Enter the weight in pounds")
  standard identifier
• scanf(lf, pounds)
  
• kilos pounds KILOS_PER_POUND
• printf(" That equals f kilos. \n, kilos)
  punctuation
• return (0)
• special
  symbol

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Executable Statements

• Data can be stored/changed in memory cells by
• Assignment statement
• variable expression () is not equal
  sign
• x x z / 6.9
• x -9
• new_x -x
• Input operations such as scanf function that
  requires
• include ltstdio.hgt

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Output Operation - printf

• printf( format string, printlist)
• printf( Hi c - your age is d\n, na,age)
• printf (It is 1th line\n)
• printf (\n and 2th line)
• printf( Enter the weight in pounds)
• scanf( lf , pounds)
• printf( f pounds was entered, pounds)

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Input Operation-scanf

• scanf (format string, input list)
• scanf (cd, initial, age)
• is using for each int, double and char
  variables (it means address of memory)
• The order of placeholders correspond to the order
  of variables in the input list
• When reading the numbers, scanf scans the digits
  and characters until it reaches non-digits, blank
  or cr. For characters only first character before
  cr is considered

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• / This program calculates ? /
• include ltstdio.hgt
• define PI 3.14159
• int main(void)
• double r,a,c
• scanf(lf, r)
• a PI r r
• c 2 PI r
• printf( ? is f cm2. \n, a)
• printf( ? is f cm. \n, c)
• return (0)

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Formating Values of Type int

• printf ( Result is 3d meters,
• Examples
• Value format display
• 234 6d 234
• 234 1d 234
• -234 6d -234
• -234 1d -234
• 234 d 234

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Formating Values of Type double

• printf ( Result is 6.2f meters,
• Examples
• Value format display
• -99.42 6.1f -99.4
• 99.999 6.2f 100.00
• -.006 8.5f -0.00600
• -.003 .3f -0.003
• -3.15 .1f -3.2
• 99.67 f 99.67

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• include ltstdio.hgt
• int main(void)
• double x 123.456
• int y12345
• printf( f .3f .1f \n,x,x,x )
• printf( 3d 5d 8d \n\n,y,y,y )
• return (0)
• 123.456 123.456 123.5
• 12345 12345 12345

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Batch Mode

• In batch mode the program gets its input from a
  data file instead of the user and sends the
  result to a data file instead of the screen. It
  is also called redirection. For example the
  following program can be run by weightconvert
  ltdata gtoutput
• / weightconvert program /
• include ltstdio.hgt
• define KILOS_PER_POUND 0.45359
• int main(void)
• double pounds, kilos
• scanf(lf, pounds)
• printf(Weight in pounds is .2f. \n, pounds)
• kilos pounds KILOS_PER_POUND
• printf(" That equals f kilos. \n, kilos)
• return (0)

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Program-controlled Input and Output files

• File pointer variable
• include ltstdio.hgt
• define KILOS_PER_POUND 0.45359
• int main(void)
• double pounds, kilos
• FILE inp, / pointer to input file /
• outp / pointer to output file /
  

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Os preparing the files for access

• / open the input and output files /
• inp fopen (aweight.txt, r)
• outp fopen (adistance.out, w)
• / get the input from file /
• fscanf(inp,lf, pounds)
• fprintf(outp, Weight in pounds is .2f. \n,
  pounds)

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• kilos pounds KILOS_PER_POUND
• / Display the result in output file /
• fprintf(output, That equals f kilos. \n,
  kilos)
• / Close files /
• fclose(inp)
• fclose(outp)
• return (0)
• We will discuss program-controlled input and
  output files in more details later.

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Common programming Errors

• Syntax Error
• Missing or variable definition
• double pounds
• instead of
• double pounds, kilos
• Last comment is not closed
• / Close files instead of / Close files /
• Correct the errors in declaration part first

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Runtime Errors and Undetected Errors

• If we use scanf for numbers and then after that
  again we use scanf for the characters, the first
  character gets different value than what we
  entered. For example in a program
• scanf (lf , radius)
• scanf (ccc, a, b, c)
• is used instead of
• scanf (ccc, a, b, c)
• scanf (lf , radius)
• If we run this program with these inputs
• I 50
• ABC
• The values stored in the variables are
• ? a b c radius
• \n A B 50
• One of the way for fixing this problem is placing
  space before first C
• scanf (lf , radius)
• scanf ( ccc, a, b, c)

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Logic Errors

• Logic errors is shown by the wrong result of the
  program. For example forgetting in the
  following statement
• scanf( dd , a, b)
• produces gt incorrect results
• Preventing logic errors is done by
• Deskchecking the algorithm and
• Debugging the program