Modes:

"r": Read mode (file must exist)
"w": Write mode (creates new file or overwrites existing)
"a": Append mode (creates new file or appends to existing)
"r+": Read and Write (file must exist)
"w+": Read and Write (creates new file or overwrites existing)
"a+": Read and Append (creates new file or appends to existing)

2. Reading from a File:

fgetc(): Reads a single character.
fgets(): Reads a string (line) until newline or EOF.
fscanf(): Reads formatted input.

3. Writing to a File:

fputc(): Writes a single character.
fputs(): Writes a string.
fprintf(): Writes formatted output.

4. Closing a File:

fclose(fp); (Closes the file associated with the file pointer and flushes any buffered data.)

C Program: Read and Write Student Records to a File

#include <stdio.h>
#include <stdlib.h> // For exit()

// Define a simple structure for student record
struct Student {
    int roll_no;
    char name[50];
    float marks;
};

int main() {
    FILE *fp;
    struct Student s;
    int choice;

    do {
        printf("\n1. Write Student Record\n");
        printf("2. Read All Student Records\n");
        printf("3. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch (choice) {
            case 1: // Write record
                fp = fopen("students.dat", "ab"); // Open in append binary mode
                if (fp == NULL) {
                    printf("Error opening file!\n");
                    exit(1);
                }

                printf("Enter Roll No: ");
                scanf("%d", &s.roll_no);
                printf("Enter Name: ");
                scanf(" %[^\n]", s.name);
                printf("Enter Marks: ");
                scanf("%f", &s.marks);

                fwrite(&s, sizeof(struct Student), 1, fp); // Write structure to file
                fclose(fp);
                printf("Record added successfully.\n");
                break;

            case 2: // Read records
                fp = fopen("students.dat", "rb"); // Open in read binary mode
                if (fp == NULL) {
                    printf("Error opening file or no records yet.\n");
                    break;
                }

                printf("\n--- Student Records from File ---\n");
                while (fread(&s, sizeof(struct Student), 1, fp) == 1) {
                    printf("Roll No: %d, Name: %s, Marks: %.2f\n", s.roll_no, s.name, s.marks);
                }
                fclose(fp);
                break;

            case 3:
                printf("Exiting program.\n");
                break;

            default:
                printf("Invalid choice. Please try again.\n");
        }
    } while (choice != 3);

    return 0;
}

Difference between Linear Search and Binary Search

Feature	Linear Search (Sequential Search)	Binary Search
Requirement	No specific requirement for the array to be sorted.	Requires the array to be sorted (ascending or descending).
Mechanism