Builder Zone in C

1. ✅ Functions in C

Functions are reusable blocks of code that perform a specific task.

🔹 User-defined Functions:

You create your own functions apart from the built-in ones.

📘 Example:

cCopyEdit#include <stdio.h>
void greet() {
    printf("Hello, Keshab!\n");
}
int main() {
    greet(); // Function call
    return 0;
}

📘 Function with parameters and return:

cCopyEditint add(int a, int b) {
    return a + b;
}
int main() {
    int result = add(3, 5);
    printf("Sum = %d\n", result);
    return 0;
}

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2. 🔁 Recursive Functions

A function that calls itself.

📘 Example: Factorial using recursion

cCopyEditint factorial(int n) {
    if(n == 0)
        return 1;
    else
        return n * factorial(n - 1);
}
int main() {
    printf("Factorial of 5 = %d\n", factorial(5));
    return 0;
}

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3. 🔢 Arrays

Arrays are collections of elements of the same data type stored in continuous memory locations.

🔹 1D Array:

cCopyEditint marks[5] = {90, 85, 88, 92, 80};

📘 Example: Sum of elements in 1D array

cCopyEditint sum = 0, i;
int arr[5] = {1, 2, 3, 4, 5};
for(i = 0; i < 5; i++) {
    sum += arr[i];
}
printf("Sum = %d\n", sum);

🔹 2D Array:

Used to store table-like data.

📘 Example: 2D Array to store marks

cCopyEditint marks[2][3] = {{80, 90, 85}, {75, 70, 95}};

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4. 📝 Strings and String Handling Functions

A string in C is an array of characters ending with a \0 (null character).

cCopyEditchar name[] = "Keshab";

🔹 Common string functions (from <string.h>):

• strlen() – Finds length
• strcpy() – Copies one string to another
• strcmp() – Compares strings
• strcat() – Concatenates strings

📘 Example:

cCopyEdit#include <stdio.h>
#include <string.h>
int main() {
    char str1[20] = "Hello ";
    char str2[] = "World";
    strcat(str1, str2);
    printf("Result: %s\n", str1);  // Output: Hello World
    return 0;
}

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5. 📍 Pointers

A pointer is a variable that stores the memory address of another variable.

🔹 Declaration:

cCopyEditint x = 10;
int *ptr = &x;

📘 Example: Print value and address

cCopyEditint x = 10;
int *p = &x;
printf("Value = %d\n", *p);     // Dereferencing
printf("Address = %p\n", p);    // Address

🔹 Pointers with Functions:

You can pass addresses to modify values in the original variable (pass-by-reference).

📘 Example:

cCopyEditvoid update(int *a) {
    *a = *a + 5;
}
int main() {
    int x = 10;
    update(&x);
    printf("Updated x = %d\n", x);
    return 0;
}

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6. 📦 Structures and Unions

✅ Structures

Used to group different data types under a single name.

📘 Example:

cCopyEditstruct Student {
    int id;
    char name[20];
    float marks;
};
int main() {
    struct Student s1 = {101, "Keshab", 95.5};
    printf("ID: %d, Name: %s, Marks: %.2f\n", s1.id, s1.name, s1.marks);
    return 0;
}

✅ Unions

Like structures but shares memory for all members (efficient for memory).

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7. ⚙️ Intermediate-level Programs

📘 Bubble Sort:

cCopyEditvoid bubbleSort(int arr[], int n) {
    for(int i = 0; i < n-1; i++)
        for(int j = 0; j < n-i-1; j++)
            if(arr[j] > arr[j+1]) {
                int temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
}

📘 Linear Search:

cCopyEditint linearSearch(int arr[], int n, int key) {
    for(int i = 0; i < n; i++)
        if(arr[i] == key)
            return i;
    return -1;
}

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✅ Summary Table

Topic	Description	Example Function
User-defined Functions	Break code into reusable parts	int add(int a, int b)
Recursive Functions	Function calling itself	factorial(n)
1D & 2D Arrays	Store multiple values	int arr[5] = {...}
Strings	Array of characters	strcat(str1, str2)
Pointers	Store addresses, enable dynamic behavior	int *p = &x;
Structures & Unions	Group different data types	struct Student {...}
Sorting & Searching	Logic-based intermediate programs	bubbleSort(arr, n)