2.3) C Input and output functions

Input and output (I/O) functions are crucial for interacting with users and external devices in C programming.

They allow your programs to receive input from users and display output to the screen or other output devices.

In C, the standard library provides a set of I/O functions to facilitate these tasks.

Standard Input/Output Library

The standard I/O library in C is provided by the <stdio.h> header file. This library includes functions that enable you to read data from standard input (usually the keyboard) and write data to standard output (usually the screen).

Input Functions

C provides the following input functions for reading data from the user:

1. scanf: Reads formatted data from standard input.

   int age;
   scanf("%d", &age);  // Read an integer from the user

2. getchar: Reads a single character from standard input.

   char ch;
   ch = getchar();     // Read a single character

Output Functions

C provides the following output functions for displaying data to the user:

1. printf: Prints formatted data to standard output.

   int x = 10;
   printf("The value of x is %d\n", x);  // Output: The value of x is 10

2. putchar: Writes a single character to standard output.

   char ch = 'A';
   putchar(ch);  // Output: A

Formatted Output

The printf function supports formatting options to control how data is displayed. Common format specifiers include:

• %d: Integer
• %f: Floating-point number
• %c: Character
• %s: String

You can also use modifiers to control width, precision, and alignment. For example:

printf("Formatted output: %5d\n", 123);    // Output: Formatted output:   123
printf("%.2f\n", 3.14159);                // Output: 3.14

Formatted Input

The scanf function also supports format specifiers for reading data in specific formats. For example:

int num;
scanf("%d", &num);     // Read an integer from the user

float price;
scanf("%f", &price);   // Read a floating-point number from the user

Buffered I/O:

C I/O operations are typically buffered, meaning that data is read/written in chunks for efficiency. The fflush function can be used to clear the buffer.

fflush(stdin);   // Clear input buffer (not recommended on some systems)
fflush(stdout);  // Clear output buffer

File I/O

Apart from standard I/O, C also provides functions for file input/output. These functions allow you to read from and write to files. Common file I/O functions include fopen, fclose, fprintf, fscanf, fputc, fgetc, etc.

#include <stdio.h>

int main() {
    FILE *file = fopen("example.txt", "w");  // Open file for writing
    if (file != NULL) {
        fprintf(file, "Hello, File I/O!");  // Write to file
        fclose(file);  // Close the file
    }

    return 0;
}