C Library – stdio.h

The stdio.h header file in C is a standard input-output library that provides functions for input and output operations. It stands for “standard input-output header”. This header file declares several functions, including printf, scanf, fopen, fclose, fread, fwrite, etc., as well as various macros and data types.

• std
  std means Standard and
  io
  io means Input-output statements
• These statements are used to get and put data on computers
• Ex-1: Can put data to a computer via the keyboard.
• Ex-2: Can get data and see that in Monitor.
• Input-output statements are used as a function in c language
• stdio.h
  stdio.h file contains that statements statements
• So if we use these functions should include
  stdio.h
  stdio.h , functions are  
  scanf()
  scanf()  ,
  printf()
  printf()   ,
  getchar()
  getchar() ,
  gets()
  gets() ,
  putchar()
  putchar() ,  
  puts()
  puts().

Here’s a brief overview of some commonly used functions and macros declared in stdio.h:

1. printf: Used to print formatted output to the standard output (usually the console).
2. scanf: Used to read formatted input from the standard input (usually the keyboard).
3. fprintf, fscanf, sprintf, sscanf: Variants of printf and scanf for performing formatted I/O operations on files or strings.
4. FILE: Data type representing a file stream used by functions like fopen, fclose, fread, fwrite, etc.
5. stdin, stdout, stderr: Predefined file streams representing standard input, standard output, and standard error respectively.

Including stdio.h at the beginning of your C program allows you to use these functions and macros. It’s an essential header file for most C programs, as it provides basic input and output capabilities.

---

scanf() 

scanf()	Description
syntax	int scanf(char *control_string, argument_list); int scanf(char *control_string, argument_list); scanf("control strings", &variable_1, &variable_2….&variable_n); scanf("control strings", &variable_1, &variable_2….&variable_n); control sting : %w %w -( % % – conversion specification indicator, W W -width of input data) & & – address of the variable
Rules	Should use comma , , to separate the different variables Same data type variable and data specifier should use.
Returns	scanf() scanf()  returns the number of data items successfully assigned a value. if an error occurs, EOF EOF  is return.
Examples	scanf("%d", &a); scanf("%d", &a); scanf("%f", &a); scanf("%f", &a); scanf("%d %f %d", &a, &b, &c); scanf("%d %f %d", &a, &b, &c); scanf("%c", &sex); scanf("%c", &sex); scanf("%s%c", &name, &sex); scanf("%s%c", &name, &sex); scanf("%4d", &a); scanf("%4d", &a); scanf("%5f", &a); scanf("%5f", &a); scanf("%20s", &name); scanf("%20s", &name);

---

printf()

• syntax :
  int printf(char *control strings, argument_list);
  int printf(char *control strings, argument_list);
• Data format :
  %w.p
  %w.p data-type
• %
  % -conversion specification indicator
• w
  w – width of the output data (optional)
• p
  p – point (dot)
• Returns:
  printf()
  printf() will return the number of characters printed count values (integer values).

Examples-1: How to print numbers, strings and character

Example	Output
printf("Character is %c \n", "A"); printf("Character is %c \n", "A");	Character is A
printf("String is %s \n" , "www.ArunEworld.com"); printf("String is %s \n" , "www.ArunEworld.com");	String is www.ArunEworld.com
printf("Float value is %f \n", 10.234); printf("Float value is %f \n", 10.234);	Float value is 10.234000
printf("Integer value is %d\n" , 150); printf("Integer value is %d\n" , 150);	Integer value is 150
printf("Double value is %lf \n", 20.123456); printf("Double value is %lf \n", 20.123456);	Double value is 20.123456
printf("Octal value is %o \n", 150); printf("Octal value is %o \n", 150);	Octal value is 226
printf("Hexadecimal value is %x \n", 150); printf("Hexadecimal value is %x \n", 150);	Hexadecimal value is 96

Examples-2: print the \n using printf()

Code

#include <stdio.h>

int main()
{
  printf("\\n");
  return printf("\n www.ArunEworld.com");
}
#include <stdio.h>

int main()
{
	printf("\\n");
	return printf("\n www.ArunEworld.com");
}

Output

\n
 www.ArunEworld.com
--------------------------------
Process exited after 1.403 seconds with return value 20
Press any key to continue . . .
\n
 www.ArunEworld.com
--------------------------------
Process exited after 1.403 seconds with return value 20
Press any key to continue . . .

Example-3: print any value without using the semicolon

Here below four example provided for print the value without semicolon. and going to print the ArunEworld string for all examples.

Method-1: Using if loop

Code:

#include <stdio.h>

void main()
{
  if(printf("ArunEworld"))
  {  
  }
}
#include <stdio.h>

void main()
{
	if(printf("ArunEworld"))
	{	
	}
}

Output:

ArunEworld

Method-2: Using while loop

Code:

#include <stdio.h>

void main()
{
  while(!printf("ArunEworld"));
  
}
#include <stdio.h>

void main()
{
	while(!printf("ArunEworld"));
	
}

Output:

ArunEworld

Explanation:

• If you observe the while loop inside, I was mentioned
  !printf("ArunEworld")
  !printf("ArunEworld"). Do you know what is the reason?
• The
  print()
  print() always returns the number of characters printed on the console.
• In the above code case, we are printing the ArunEworld string and the string size is 10 characters.
• When the first time executes the program in the while loop,
  print()
  print() will return 10 decimal value. so the program will continuously run like an infinite loop.
• In order to avoid infinite times print the string, here mentioned
  !
  ! symbol so whatever positive value getting from
  print()
  print(), it will be considered as the negative value of while loop after first execution and it will stop the next execution.

Method-3: Using switch case

Code:

#include <stdio.h>

void main()
{
  switch(printf("ArunEworld"))
  {
    
  }  
}
#include <stdio.h>

void main()
{
	switch(printf("ArunEworld"))
	{
		
	}	
}

Output:

ArunEworld
--------------------------------
Process exited after 0.7511 seconds with return value 10
Press any key to continue . . .
ArunEworld
--------------------------------
Process exited after 0.7511 seconds with return value 10
Press any key to continue . . .

Examples-4: Different width and Different Type

Print the decimal value with different width (Ex-1)

Code

#include <stdio.h>

int main()
{
	int x=8;
	printf("%d\n\r",x);
	printf("%3d\n\r",x);
	printf("%5d\n\r",x);
	printf("%-5d\n\r",x);
	printf("%07d\n\r",x);
	printf("%4d\n\r",-x);
	return printf("www.ArunEworld.com");
}

Output

8
  8
    8
8
0000008
  -8
www.ArunEworld.com
--------------------------------
Process exited after 0.3254 seconds with return value 18
Press any key to continue . . .
8
  8
    8
8
0000008
  -8
www.ArunEworld.com
--------------------------------
Process exited after 0.3254 seconds with return value 18
Press any key to continue . . .

Print the different type with different width (Ex-2)

Code:

#include <stdio.h>

int main(void)
{
    printf("Strings:\n");
    const char* s = "Hello";
    printf("printnig S is : % ");
    printf(s);
  printf("\n");
    printf("\t.%10s.\n\t.%-10s.\n\t.%*s.\n", s, s, 10, s);

    printf("Characters:\t%c %%\n", 65);

    printf("Integers\n");
    printf("Decimal:\t%i %d %.6i %i %.0i %+i %u\n", 1, 2, 3, 0, 0, 4, -1);
    printf("Hexadecimal:\t%x %x %X %#x\n", 5, 10, 10, 6);
    printf("Octal:\t%o %#o %#o\n", 10, 10, 4);

    printf("Floating point\n");
    printf("Rounding:\t%f %.0f %.32f\n", 1.5, 1.5, 1.3);
    printf("Padding:\t%05.2f %.2f %5.2f\n", 1.5, 1.5, 1.5);
    printf("Scientific:\t%E %e\n", 1.5, 1.5);
    printf("Hexadecimal:\t%a %A\n", 1.5, 1.5);
}
#include <stdio.h>

int main(void)
{
    printf("Strings:\n");
    const char* s = "Hello";
    printf("printnig S is : % ");
    printf(s);
	printf("\n");
    printf("\t.%10s.\n\t.%-10s.\n\t.%*s.\n", s, s, 10, s);

    printf("Characters:\t%c %%\n", 65);

    printf("Integers\n");
    printf("Decimal:\t%i %d %.6i %i %.0i %+i %u\n", 1, 2, 3, 0, 0, 4, -1);
    printf("Hexadecimal:\t%x %x %X %#x\n", 5, 10, 10, 6);
    printf("Octal:\t%o %#o %#o\n", 10, 10, 4);

    printf("Floating point\n");
    printf("Rounding:\t%f %.0f %.32f\n", 1.5, 1.5, 1.3);
    printf("Padding:\t%05.2f %.2f %5.2f\n", 1.5, 1.5, 1.5);
    printf("Scientific:\t%E %e\n", 1.5, 1.5);
    printf("Hexadecimal:\t%a %A\n", 1.5, 1.5);
}

Output:

Strings:
printnig S is : Hello
        .     Hello.
        .Hello     .
        .     Hello.
Characters:     A %
Integers
Decimal:        1 2 000003 0  +4 4294967295
Hexadecimal:    5 a A 0x6
Octal:  12 012 04
Floating point
Rounding:       1.500000 2 1.30000000000000000000000000000000
Padding:        01.50 1.50  1.50
Scientific:     1.500000E+000 1.500000e+000
Hexadecimal:    0x1.800000p+0 0X1.800000P+0

--------------------------------
Process exited after 2.748 seconds with return value 41
Press any key to continue . . .
Strings:
printnig S is : Hello
        .     Hello.
        .Hello     .
        .     Hello.
Characters:     A %
Integers
Decimal:        1 2 000003 0  +4 4294967295
Hexadecimal:    5 a A 0x6
Octal:  12 012 04
Floating point
Rounding:       1.500000 2 1.30000000000000000000000000000000
Padding:        01.50 1.50  1.50
Scientific:     1.500000E+000 1.500000e+000
Hexadecimal:    0x1.800000p+0 0X1.800000P+0

--------------------------------
Process exited after 2.748 seconds with return value 41
Press any key to continue . . .

Print the different type with different width (Ex-3)

Code:

#include <stdio.h>

int main()
{
   printf ("Characters    : %c %c \n", 'a', 65);
   printf ("Decimals    : %d %ld\n", 1977, 650000L);
   printf ("Preceding with blanks  : %10d \n", 1977);
   printf ("Preceding with zeros  : %010d \n", 1977);
   printf ("Some different radices  : %d %x %o %#x %#o \n", 100, 100, 100, 100, 100);
   printf ("floats      : %4.2f %+.0e %E \n", 3.1416, 3.1416, 3.1416);
   printf ("Width trick    : %*d \n", 5, 10);
   printf ("%s \n", "A string");
   return 0;
}
#include <stdio.h>

int main()
{
   printf ("Characters		: %c %c \n", 'a', 65);
   printf ("Decimals		: %d %ld\n", 1977, 650000L);
   printf ("Preceding with blanks	: %10d \n", 1977);
   printf ("Preceding with zeros	: %010d \n", 1977);
   printf ("Some different radices	: %d %x %o %#x %#o \n", 100, 100, 100, 100, 100);
   printf ("floats			: %4.2f %+.0e %E \n", 3.1416, 3.1416, 3.1416);
   printf ("Width trick		: %*d \n", 5, 10);
   printf ("%s \n", "A string");
   return 0;
}

Output:

Characters              : a A
Decimals                : 1977 650000
Preceding with blanks   :       1977
Preceding with zeros    : 0000001977
Some different radices  : 100 64 144 0x64 0144
floats                  : 3.14 +3e+000 3.141600E+000
Width trick             :    10
A string

--------------------------------
Process exited after 2.739 seconds with return value 0
Press any key to continue . . .
Characters              : a A
Decimals                : 1977 650000
Preceding with blanks   :       1977
Preceding with zeros    : 0000001977
Some different radices  : 100 64 144 0x64 0144
floats                  : 3.14 +3e+000 3.141600E+000
Width trick             :    10
A string

--------------------------------
Process exited after 2.739 seconds with return value 0
Press any key to continue . . .

Examples-5: printf() return type understanding

Code:

#include<stdio.h>
int main()
{
   printf("%x", -1<<1);
   getchar();
   return 0;
}
#include<stdio.h>
int main()
{
   printf("%x", -1<<1);
   getchar();
   return 0;
}

Output: Dependent on the compiler. For 32 bit compiler it would be fffffffe and for 16 bit it would be fffe.

Example-6: Printf() and Macro

# include <stdio.h>
# define display_in_macro  "%s ArunEworld "
main()
{
   printf(display_in_macro, display_in_macro);
   getchar();
   return 0;
}
# include <stdio.h>
# define display_in_macro  "%s ArunEworld "
main()
{
   printf(display_in_macro, display_in_macro);
   getchar();
   return 0;
}

Output :

%s ArunEworld ArunEworld
Explanation: After a pre-processing phase of compilation, the printf statement will become "%s ArunEworld " in macro place.

Example 7: Print the char pointer string

#include <stdio.h>
int main(void) 
{
    char *p = "ArunEworld";
    printf(p);
    return 0;
}
#include <stdio.h>
int main(void) 
{
    char *p = "ArunEworld";
    printf(p);
    return 0;
}

Output:

ArunEworld

Compiler [Warning]: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]

sprintf()

• Syntax:
  sprintf()
  sprintf()
• Description: Prints the formatted output onto the character array.

Example

int main(void)
{
    char buf[30];
    int x = 1, y = 3;
    int z = x * y;
    sprintf(buf, "Mul : %d * %d = %d", x, y, z);

    // into buffer instead of printing on stdout
    printf("%s", buf);

    return 0;
}

/* Output: Mul : 1 * 3 = 3 */

---

stdio.h Library Other Functions Syntax

Functions	Syntax	Descriptions
fputc() fputc()	fputc(character, file_pointer); fputc(character, file_pointer);
getchar() getchar()	var = getchar(); getchar();
putchar() putchar()	putchar(var); putchar(var);
puts() puts()	puts(var) puts(var)	Example: puts(“ ArunEworld ArunEworld“)

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