Input and Output

This document covers Input and Output in C.

Input and output (I/O) operations are essential for interacting with users and handling data in C programs. The C standard library provides functions like printf() for output and scanf() for input. Additionally, escape sequences help in formatting output effectively.

Output using printf()

The printf() function displays formatted output on the screen. It supports various format specifiers to print different types of data.

Syntax

printf("Some text is: %fs \n", var_name); 

info

fs is the format specifier depending of the type of the variable.

Example

#include <stdio.h>
int main() {
    int age = 25;
    printf("Your age is: %d\n", age);
    return 0;
}

info

Here, %d is a format specifier that tells printf() to print an integer value.

Input using scanf()

The scanf() function is used to take user input. The & (address-of) operator is required when storing input in variables.

Syntax

scanf("%fs", var_name); //where fs is the format specifier

Example:

#include <stdio.h>
int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    printf("You entered: %d\n", age);
    return 0;
}

info

Here, %d is used for reading an integer input from the user.

Common Format Specifiers

Specifier	Data Type	Example
%d	Integer (int)	printf("%d", 10);
%f	Floating-point (float)	printf("%.2f", 3.14);
%c	Character (char)	printf("%c", 'A');
%s	String (char[])	printf("%s", "Hello");
%lf	Double (double)	printf("%lf", 3.14159);

Example:

float pi = 3.14159;
printf("Value of Pi: %.2f\n", pi);

info

Here, %.2f ensures that only two decimal places of pi are printed.

Escape Sequences

Escape sequences allow special characters to be included in strings while maintaining readability and proper formatting.

Escape Sequence	Meaning	Example Output
\n	Newline (moves to the next line)	Hello,\nWorld! → Hello, <br> World!
\t	Tab space (adds horizontal spacing)	Tab\tSpace → Tab Space
\"	Double quote (use inside a string)	\"Hello\" → "Hello"
\\	Backslash (prints \ character)	\\path\\to\\file → \path\to\file

Example:

printf("Hello,\nWorld!\n"); // Prints on two lines
printf("Tab\tSpace\n"); // Adds a tab space

info

• The \n escape sequence moves the cursor to a new line.

• The \t escape sequence inserts a tab space for indentation.

Character Inptu & Output using getchar() & putchar()

• getchar() is used to read a single character from standard input (keyboard).
• putchar() is used to display a single character on the screen.

Example:

#include <stdio.h>
int main() {
    char ch;
    printf("Enter a character: ");
    ch = getchar(); // Reads a single character
    printf("You entered: ");
    putchar(ch); // Prints the character
    printf("\n");
    return 0;
}

info

• getchar() waits for the user to input a character and stores it in ch.

• putchar() prints the character stored in ch.

String Input and Output using fgets() and puts()

• fgets() is used to read a line of text (string) from standard input.
• puts() is used to print a string with an automatic newline at the end.

Example:

#include <stdio.h>
int main() {
    char name[50];
    printf("Enter your name: ");
    fgets(name, sizeof(name), stdin); // Reads a line of text
    printf("Hello, ");
    puts(name); // Prints the string with a newline
    return 0;
}

info

• fgets() reads a full line of input and prevents buffer overflow.

• puts() prints a string and automatically adds a newline.