C <stdio.h>

C <stdio.h>: Standard Input/Output Library

The <stdio.h> header file is the most commonly used library in the C programming language. It stands for Standard Input Output. It contains the core functions needed to read input from the user (like a keyboard) and print output to the screen or a file.

1. Core Output Functions

• printf(): Prints formatted data to the standard output (usually the console screen). It is the most heavily used function for displaying text and variables.
• puts(): Prints a string to the console, automatically appending a newline character (\n) at the end.
• putchar(): Prints a single character to the console.

#include <stdio.h>

int main() {
    printf("Formatted output: %d, %s\n", 100, "Hello");
    puts("This prints a string with a newline automatically.");
    putchar('A'); // Prints a single char
    return 0;
}

2. Core Input Functions

• scanf(): Reads formatted data from the standard input (usually the keyboard). It requires pointers (using the & address-of operator) to store the retrieved values in variables.
• gets() / fgets(): Reads a line of text (string) from the user. fgets() is preferred because it prevents buffer overflow vulnerabilities by limiting the number of characters read.
• getchar(): Reads a single character from the user input.

#include <stdio.h>

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age); // Reading an integer
    printf("You are %d years old.\n", age);
    return 0;
}

3. File I/O Functions

<stdio.h> is also responsible for all file handling operations in C:

• fopen(): Opens a file.
• fclose(): Closes a file.
• fprintf(): Writes formatted data to a file.
• fscanf(): Reads formatted data from a file.