3. First C Program

First C Program

======================================================================
#include <stdio.h>
#include <conio.h>
void main()
  {
     int a,b,c;
     clrscr();
     a=10;
     b=20;
     c=a+b;
     printf("%d",c);
     getch();
  }
======================================================================

Program Explanation

#include <stdio.h>
#include <conio.h>
                    are used to add required header files.

void main()  
                   main function which tells the compiler for entry point of program

{   }   
                start and end of a block


int a,b,c;
                declares thee variables (a,b,c) of type signed integer each of 16 bytes.

clrscr()
                a function being used to clear the output screen. it works only when conio.h header file is included using #include

a=10;
b=20;
              stores 10 in a and 20 in b

c=a+b;
              adds value of a and b and stores it in c

printf("%d",c);
              prints the value of c on the output screen. it is available only if stdio.h header file is included.

getch();
              A function used to read a single character from keyboard  but at here it is used to make the output static. the output screen generally displayed only for a fraction of second after execution. and then program terminates and c IDE is displayed again back. To prevent getch() is used because it waits until user doesn't press a key and in results it prevent termination of protram.

How to use printf

printf is used for formatted output. The general syntax of printf is

printf("control string",list of variables);

Control string consists of 

    

    Type Specifiers               %d  %f    %c etc

    Control Characters         \n \r \t etc

    General Text                  anything other is considered as general text

    Let us create printf statement for the output (for above program)

    30 is obtained by adding 10 and 20

    Step 1.

       Replace each numeric or character value coming from variable with corresponding type specifier.

       the result will be

       %d is obtained by adding %d and %d

       becaues 30 comes from c, c is integer, , %d is type specifier for int

       similar is the case for 10 and 20

      now list of the variables will be c,a,b because first %d is for c , second is for a and third is for a. thus the final printf statement for the required output will be

printf("%d is obtained by adding %d and %d",c,a,b);

and the complete required program will be

======================================================================
#include <stdio.h>
#include <conio.h>
void main()
  {
     int a,b,c;
     clrscr();
     a=10;
     b=20;
     c=a+b;
     printf("%d is obtained by adding %d and %d",c,a,b);
     getch();
  }
======================================================================

    

control characters are used to control the output behavior 

ie \n i use to print remaining text in new line.

the complete escape sequence is

Escape sequence	Hex value	Connotation
\a	07	Alarm (Beep, Bell)
\b	08	Backspace
\f	0C	Formfeed
\n	0A	Newline (Line Feed); see notes below
\r	0D	Carriage Return
\t	09	Horizontal Tab
\v	0B	Vertical Tab
\\	5C	Backslash
\'	27	Single quotation mark
\"	22	Double quotation mark
\?	3F	Question mark
\0	00	Null (string terminator)

  printf("Hello\nWorld");  // will print World in next line

  will print

  Hello

  World

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