3. Input & Output

1. Formatted Input / Output

printf()

Used to print formatted output to the standard output screen (console).

Syntax: printf("format_string", variables...);

int age = 20;
printf("I am %d years old.", age); // %d is the format specifier for integer

scanf()

Used to take formatted input from the standard input (keyboard). You must pass the memory address of the variable using the & (address-of) operator.

Syntax: scanf("format_string", &variables...);

int age;
printf("Enter your age: ");
scanf("%d", &age); // Requires '&' to store the value at the variable's memory address

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2. Unformatted Input / Output (Characters & Strings)

These functions do not require format specifiers like %d or %s.

Character I/O

getchar()

Reads a single character from the keyboard. It waits for the user to press Enter. Syntax: char c = getchar();

putchar()

Prints a single character to the console. Syntax: putchar(character_variable);

Example:

#include <stdio.h>

int main() {
    char ch;
    printf("Enter a character: ");
    ch = getchar(); // Reads one character
    
    printf("You entered: ");
    putchar(ch);    // Prints one character
    printf("\n");
    return 0;
}

String I/O

gets() (Warning: Unsafe and Deprecated)

Reads a line of text (string) from standard input until a newline is placed. It is dangerous because it doesn't check for array bounds, which can lead to buffer overflow attacks. Syntax: gets(string_variable);

fgets() (Safe Alternative to gets)

Reads a string with a specified size limit from a specified stream (like stdin for keyboard). It is safer than gets. Syntax: fgets(string_array, max_length, input_stream);

puts()

Writes a string to the console and automatically appends a newline character (\n) at the end. Syntax: puts(string_variable);

Example:

#include <stdio.h>

int main() {
    char name[50];
    
    printf("Enter your full name: ");
    // Using fgets instead of gets for safety
    fgets(name, sizeof(name), stdin); 
    
    printf("Your name is: ");
    puts(name); // Automatically adds a newline
    
    return 0;
}