Review & Practical Sessions: C Programming Mastery

Key Concepts Recap

1. Syntax and Structure Review

C programs follow a strict structure:

#include <stdio.h>  // Preprocessor directive
int main() {        // Main function (entry point)
    // Declarations & statements
    return 0;       // Exit status
}

Visual: Program flow as a finite state machine (start → declarations → execution → exit).

stateDiagram-v2
    [*] --> Start: main()
    Start --> Declarations: variables, types
    Declarations --> Execution: statements
    Execution --> Exit: return 0
    Exit --> [*]

2. Data Types and Memory

Real-world tie: Khalti’s transaction system uses int for order IDs and float for amounts (e.g., float balance = 5000.00;).

Practical Exercises

Exercise 1: Student Record System

Task: Store 10 student names (strings) and marks (floats) in arrays, then compute average. Solution:

#include <stdio.h>
#define N 10

int main() {
    char names[N][50];
    float marks[N], sum = 0.0;
    for (int i = 0; i < N; i++) {
        printf("Enter name %d: ", i+1);
        scanf("%s", names[i]);
        printf("Enter marks: ");
        scanf("%f", &marks[i]);
        sum += marks[i];
    }
    printf("Average: %.2f\n", sum/N);
    return 0;
}

Trace Table:

Visual: Array state after input:

graph LR
    A["names[0]"] -->|"Ram"| B["names[1]"] -->|"Sita"| C["..."]
    D["marks[0]"] -->|"85.5"| E["marks[1]"] -->|"90.0"| F["..."]

Exercise 2: Bank Transaction Simulator

Task: Simulate a bank account with deposit/withdraw using structures and file handling. Code:

#include <stdio.h>
typedef struct {
    char name[50];
    float balance;
} Account;

void saveToFile(Account acc) {
    FILE *fp = fopen("account.dat", "ab");
    fwrite(&acc, sizeof(Account), 1, fp);
    fclose(fp);
}

int main() {
    Account acc = {"John", 1000.0};
    saveToFile(acc);
    printf("Saved to file.\n");
    return 0;
}

File State After Execution:

graph TD
    A["account.dat"] -->|"Binary Data"| B["John\n1000.00"]

Real-world tie: NMB Bank’s ATM uses similar file handling to store transaction histories.

Common Pitfalls and Fixes

In the Real World

1. eSewa’s Payment Queue

   • Uses FIFO queues (via linked lists) to process transactions in order.
   • Example: When you pay a bill, your request joins the queue until processed.

2. Pathao’s Ride Allocation

   • Hash tables map driver IDs to their current location for fast lookup.
   • Example: When you request a ride, the app checks available drivers in O(1) time.

3. NTC’s Network Routing

   • Graph algorithms (Dijkstra’s) find the shortest path for data packets.
   • Example: Your internet traffic takes the fastest route to Google’s servers.

Exam Tip

• For TU/PU exams:
  • Code tracing: Always show the state after each step (e.g., array/pointer changes).
  • File handling: Remember modes ("r", "w", "a") and fopen checks.
  • Pointers: Draw memory diagrams for questions on *ptr vs &var.
  • Structures: Use them for real-world data (e.g., struct Student { char name[50]; int marks; };).
• NEB tips:
  • Explain time complexity (e.g., "This loop runs in O(n) time").
  • For debugging questions, comment each step in your answer.

Final Challenge: Write a program to find the longest word in a text file (use fgets + string functions). Hint: Compare lengths using strlen().