When we say Input, it means to feed some data into a program. An input can be given in the form of a file or from the command line. C programming provides a set of built-in functions to read the given input and feed it to the program as per requirement.

When we say Output, it means to display some data on screen, printer, or in any file. C programming provides a set of built-in functions to output the data on the computer screen as well as to save it in text or binary files.

The standard input-output header file, named stdio.h contains the definition of the functions printf() and scanf(), which are used to display output on screen and to take input from user respectively.

printf() function in C language

• In C programming language, printf() function is used to print the “character, string, float, integer, octal and hexadecimal values” onto the output screen.
• We use printf() function with %d format specifier to display the value of an integer variable.
• Similarly %c is used to display character, %f for float variable, %s for string variable, %lf for double and %x for hexadecimal variable.
• To generate a newline,we use “\n” in C printf() statement.

scanf() function in C language

• In C programming language, scanf() function is used to read character, string, numeric data from keyboard

Note:

C language is case sensitive. For example, printf() and scanf() are different from Printf() and Scanf(). All characters in printf() and scanf() functions must be in lower case.

Example of prinf() and scanf()

#include<stdio.h>

void main()
{
    // defining a variable
    int i;
    /* 
        displaying message on the screen
        asking the user to input a value
    */
    printf("Please enter a value...");
    /*
        reading the value entered by the user
    */
    scanf("%d", &i);
    /*
        displaying the number as output
    */
    printf( "\nYou entered: %d", i);
}

You must be wondering what is the purpose of %d and & inside the scanf() or printf() functions. It is known as format string and this informs the scanf() function, what type of input to expect and in printf() it is used to give a heads up to the compiler, what type of output to expect.

The format specifier %d is used in scanf() statement. So that, the value entered is received as an integer.

Ampersand is used before variable name "i" in scanf() statement as &i.

It is just like in a pointer which is used to point to the variable