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 means Standard and 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 file contains that statements statements
• So if we use these functions should include stdio.h , functions are  scanf()  , printf()   , getchar() , gets() , putchar() ,  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.

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scanf() 

scanf()	Description
syntax	int scanf(char *control_string, argument_list); scanf("control strings", &variable_1, &variable_2….&variable_n); control sting : %w -(% – conversion specification indicator, 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()  returns the number of data items successfully assigned a value. if an error occurs, EOF  is return.
Examples	scanf("%d", &a); scanf("%f", &a); scanf("%d %f %d", &a, &b, &c); scanf("%c", &sex); scanf("%s%c", &name, &sex); scanf("%4d", &a); scanf("%5f", &a); scanf("%20s", &name);

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printf()

• syntax : int printf(char *control strings, argument_list);
• Data format : %w.p data-type
• % -conversion specification indicator
• w – width of the output data (optional)
• p – point (dot)
• Returns: 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");	Character is A
printf("String is %s \n" , "www.ArunEworld.com");	String is www.ArunEworld.com
printf("Float value is %f \n", 10.234);	Float value is 10.234000
printf("Integer value is %d\n" , 150);	Integer value is 150
printf("Double value is %lf \n", 20.123456);	Double value is 20.123456
printf("Octal value is %o \n", 150);	Octal value is 226
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");
}

Output

\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"))
	{	
	}
}

Output: ArunEworld

Method-2: Using while loop

Code:

#include <stdio.h>

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

Output: ArunEworld

Explanation:

• If you observe the while loop inside, I was mentioned !printf("ArunEworld"). Do you know what is the reason?
• The 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() 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(), 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"))
	{
		
	}	
}

Output:

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 . . .

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);
}

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 . . .

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;
}

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 . . .

Examples-5: printf() return type understanding

Code:

#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;
}

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;
}

Output: ArunEworld

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

sprintf()

• Syntax: 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 */

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stdio.h Library Other Functions Syntax

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

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