C Input and Output (I/O)

As we all know, the three essential functions of a computer are reading, processing, and writing data. Most C programs take data as input, and then after processing, the processed data is displayed, which is called information. This tutorial will teach you various predefined C functions to read and print data.

Table of Contents

To read and print data, you can use the predefined functions scanf() and printf() in C programs.

Example:

#include <stdio.h>

void main()
{
    int a, b, c;
    printf("Please enter any two numbers: \n");
    scanf("%d %d", &a, &b);
    c = a + b;
    printf("The addition of two number is: %d", c);
}

Output:

Please enter any two numbers:
12
3
The addition of two number is:15

In the above program, the scanf() function takes input from the user, and the printf() function displays the output result on the screen.

Managing Input/Output

I/O operations are helpful for a program to interact with users. C stdlib is the standard C library for input-output operations. Two essential streams play their role when dealing with input-output operations in C. These are:

  1. Standard Input (stdin)
  2. Standard Output (stdout)

Standard input or stdin is used for taking input from devices such as the keyboard as a data stream. Standard output or stdout is used to give output to a device such as a monitor. For I/O functionality, programmers must include the stdio header file within the program.

Reading Character In C

The easiest and simplest of all I/O operations are taking a character as input by reading that character from standard input (keyboard). getchar() function can be used to read a single character. This function is an alternative to scanf() function.

Syntax:

var_name = getchar();

Example:

#include<stdio.h>

void main()
{
    char title;
    title = getchar();
}

There is another function to do that task for files: getc() which is used to accept a character from standard input.

Syntax:

int getc(FILE *stream);

Writing Character In C

Similar to getchar(), there is another function that is used to write characters, but one at a time.

Syntax:

putchar(var_name);

Example:

#include<stdio.h>

void main()
{
    char result = 'P';
    putchar(result);
    putchar('\n');
}

Similarly, there is another function putc() which is used for sending a single character to the standard output.

Syntax:

int putc(int c, FILE *stream);

Formatted Input

It refers to input data that has been arranged in a specific format. This is possible in C using scanf() function. We have already encountered this and are familiar with this function.

Syntax:

scanf("control string", arg1, arg2, ..., argn);

The field specification for reading integer input numbers is:

%w sd

Here the % sign denotes the conversion specification; w signifies the integer number that defines the field width of the number to be read. d defines the number to be read in integer format.

Example:

#include<stdio.h>

void main()
{
    int var1= 60;
    int var2= 1234;
    scanf("%2d %5d", &var1, &var2);
}

Input data items should have to be separated by spaces, tabs, or a new line, and the punctuation marks are not counted as separators.

Reading and Writing Strings in C

There are two popular library functions for dealing with strings in C: gets() and puts().

gets: The char *gets(char *str) reads a line from stdin, keeps the string pointed to by the str, and is terminated when the new line is read, or EOF is reached. The declaration of gets() function is:

Syntax:

char *gets(char *str);

Where str is a pointer to an array of characters where C strings are stored.

puts: The function - int puts(const char *str) is used to write a string to stdout, but it does not include null characters. A new line character needs to be appended to the output. The declaration is:

Syntax:

int puts(const char *str)

where the str is the string to be written in C.