What is the difference between static and extern storage classes in C?

static variables retain their values across function calls and are localized to the defining block/file. extern variables are global variables declared in another file/scope, shared across compilation units.

Why does Call by Reference modify actual arguments in main()?

Call by Reference passes memory addresses of variables to function pointers. Dereferencing these pointers inside the function directly manipulates the caller's stack frame memory.

MAKAUT C Programming Unit 3: Functions, Storage Classes, Pointers & 1D Arrays Masterclass

Q: What is an Adam Number?

An Adam Number is a number where the square of the reverse of the number equals the reverse of the square of the number (e.g. 12^2 = 144, 21^2 = 441, reverse of 441 is 144).

Unit 3 of MAKAUT C Programming (PPS-II) shifts focus from basic control flow to structured modular software design. Pointers, call-by-reference mechanics, storage classes (static, extern), and 1D array operations are heavily tested in both university semester examinations and campus technical interviews (TCS NQT, Cognizant, Wipro, LTIMindtree).

This guide unpacks the entire Unit 3 syllabus with clear stack activation frame diagrams, storage class memory tables, and 5+ solved high-scoring MAKAUT exam programs.

---

1. Modular Programming & Functions

A function is a self-contained block of statements designed to perform a specific task.

Components of a Function:

Function Prototype: Informs compiler of function name, parameters, and return type before invocation.
Function Definition: Contains actual executable code body.
Function Call: Invokes the function, passing actual arguments and allocating a stack frame.

---

2. Storage Classes in C: auto, register, static, extern

IMPORTANT

Storage classes dictate 4 properties of a variable: Storage Location (RAM/Register), Default Initial Value, Scope, and Lifetime. Questions asking to differentiate between static and extern appear almost every year in Group B (5 Marks).

Storage Class	Location	Default Initial Value	Scope	Lifetime
`auto`	Stack RAM	Garbage Value	Local to block	Block execution duration
`register`	CPU Register (if free)	Garbage Value	Local to block	Block execution duration
`static`	Data Segment (RAM)	Zero (`0`)	Local to block	Retained across function calls
`extern`	Data Segment (RAM)	Zero (`0`)	Global across files	Entire application lifetime

---

3. Parameter Passing: Call by Value vs Call by Reference

1Call by Value(Values Copied):
2Main Stack Frame [x = 10, y = 20] ---> Copy ---> Function Stack Frame [a = 10, b = 20]
3 
4Call by Reference(Memory Addresses Passed):
5Main Stack Frame [x = 10, y = 20] <--- Dereference --- Function Stack Frame [pA = &x, pB = &y]

Swapping Program: Call by Value vs Call by Reference

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3void swapByValue(int a, int b) {
4    int temp = a;
5    a = b;
6    b = temp;
7}
8 
9void swapByReference(int *a, int *b) {
10    int temp = *a;
11    *a = *b;
12    *b = temp;
13}
14 
15int main() {
16    int x = 10, y = 20;
17 
18    swapByValue(x, y);
19    printf("After Call by Value:     x = %d, y = %d\n", x, y); // Unchanged: 10, 20
20 
21    swapByReference(&x, &y);
22    printf("After Call by Reference: x = %d, y = %d\n", x, y); // Swapped: 20, 10
23 
24    return 0;
25}

---

4. 1D Array Fundamentals & Pointer-Array Duality

An array stores elements of the same data type in contiguous memory locations.

Key Equivalences:

arr (array name) decays into pointer to first element (&arr[0]).
arr[i] \equiv *(arr + i).
&arr[i] \equiv (arr + i).

---

5. Solved High-Scoring MAKAUT Exam Programs

Program 1: Finding 2nd Largest & 2nd Smallest Array Elements (Single Pass O(N))

*Exam Context: Group B / Group C (10 Marks)*

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><limits.h>
3 
4int main() {
5    int arr[] = {12, 35, 1, 10, 34, 1};
6    int n = sizeof(arr) / sizeof(arr[0]);
7 
8    int max1 = INT_MIN, max2 = INT_MIN;
9    int min1 = INT_MAX, min2 = INT_MAX;
10 
11    for (int i = 0; i < n; i++) {
12        // Update Max values
13        if (arr[i] > max1) {
14            max2 = max1;
15            max1 = arr[i];
16        } else if (arr[i] > max2 && arr[i] != max1) {
17            max2 = arr[i];
18        }
19 
20        // Update Min values
21        if (arr[i] < min1) {
22            min2 = min1;
23            min1 = arr[i];
24        } else if (arr[i] < min2 && arr[i] != min1) {
25            min2 = arr[i];
26        }
27    }
28 
29    printf("2nd Largest Element  = %d\n", max2);
30    printf("2nd Smallest Element = %d\n", min2);
31    return 0;
32}

---

Program 2: Merging Two Sorted Arrays into a Third Sorted Array

*Exam Context: Group C (10 Marks)*

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3void mergeSortedArrays(int arr1[], int n1, int arr2[], int n2, int result[]) {
4    int i = 0, j = 0, k = 0;
5 
6    while (i < n1 && j < n2) {
7        if (arr1[i] <= arr2[j]) {
8            result[k++] = arr1[i++];
9        } else {
10            result[k++] = arr2[j++];
11        }
12    }
13 
14    // Copy remaining elements
15    while (i < n1) result[k++] = arr1[i++];
16    while (j < n2) result[k++] = arr2[j++];
17}
18 
19int main() {
20    int arr1[] = {1, 3, 5, 7};
21    int arr2[] = {2, 4, 6, 8, 10};
22    int n1 = 4, n2 = 5;
23    int result[9];
24 
25    mergeSortedArrays(arr1, n1, arr2, n2, result);
26 
27    printf("Merged Sorted Array: ");
28    for (int i = 0; i < 9; i++) {
29        printf("%d ", result[i]);
30    }
31    printf("\n");
32    return 0;
33}

---

Program 3: Adam Number Verification

An Adam Number is a number where the square of the reverse of the number equals the reverse of the square of the number (e.g., 12^2 = 144; reverse of 12 is 21; 21^2 = 441; reverse of 441 is 144).

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3int reverse(int num) {
4    int rev = 0;
5    while (num > 0) {
6        rev = rev * 10 + (num % 10);
7        num /= 10;
8    }
9    return rev;
10}
11 
12int main() {
13    int num;
14    printf("Enter integer: ");
15    scanf("%d", &num);
16 
17    int sq1 = num * num;
18    int revNum = reverse(num);
19    int sq2 = revNum * revNum;
20 
21    if (sq1 == reverse(sq2))
22        printf("%d is an Adam Number.\n", num);
23    else
24        printf("%d is NOT an Adam Number.\n", num);
25 
26    return 0;
27}

---

6. Key Takeaways for Unit 3

Never return pointers to local automatic stack variables from a function. Local stack memory is deallocated upon function return, resulting in a dangling pointer.
Pass large arrays via pointers (const int *arr) to avoid overhead from copying array elements.

This guide unpacks the entire Unit 3 syllabus with clear stack activation frame diagrams, storage class memory tables, and 5+ solved high-scoring MAKAUT exam programs.

---

1. Modular Programming & Functions

A function is a self-contained block of statements designed to perform a specific task.

Components of a Function:

Function Prototype: Informs compiler of function name, parameters, and return type before invocation.
Function Definition: Contains actual executable code body.
Function Call: Invokes the function, passing actual arguments and allocating a stack frame.

---

2. Storage Classes in C: auto, register, static, extern

IMPORTANT

Storage Class	Location	Default Initial Value	Scope	Lifetime
`auto`	Stack RAM	Garbage Value	Local to block	Block execution duration
`register`	CPU Register (if free)	Garbage Value	Local to block	Block execution duration
`static`	Data Segment (RAM)	Zero (`0`)	Local to block	Retained across function calls
`extern`	Data Segment (RAM)	Zero (`0`)	Global across files	Entire application lifetime

---

3. Parameter Passing: Call by Value vs Call by Reference

1Call by Value(Values Copied):
2Main Stack Frame [x = 10, y = 20] ---> Copy ---> Function Stack Frame [a = 10, b = 20]
3 
4Call by Reference(Memory Addresses Passed):
5Main Stack Frame [x = 10, y = 20] <--- Dereference --- Function Stack Frame [pA = &x, pB = &y]

Swapping Program: Call by Value vs Call by Reference

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3void swapByValue(int a, int b) {
4    int temp = a;
5    a = b;
6    b = temp;
7}
8 
9void swapByReference(int *a, int *b) {
10    int temp = *a;
11    *a = *b;
12    *b = temp;
13}
14 
15int main() {
16    int x = 10, y = 20;
17 
18    swapByValue(x, y);
19    printf("After Call by Value:     x = %d, y = %d\n", x, y); // Unchanged: 10, 20
20 
21    swapByReference(&x, &y);
22    printf("After Call by Reference: x = %d, y = %d\n", x, y); // Swapped: 20, 10
23 
24    return 0;
25}

---

4. 1D Array Fundamentals & Pointer-Array Duality

An array stores elements of the same data type in contiguous memory locations.

Key Equivalences:

arr (array name) decays into pointer to first element (&arr[0]).
arr[i] \equiv *(arr + i).
&arr[i] \equiv (arr + i).

---

5. Solved High-Scoring MAKAUT Exam Programs

Program 1: Finding 2nd Largest & 2nd Smallest Array Elements (Single Pass O(N))

*Exam Context: Group B / Group C (10 Marks)*

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><limits.h>
3 
4int main() {
5    int arr[] = {12, 35, 1, 10, 34, 1};
6    int n = sizeof(arr) / sizeof(arr[0]);
7 
8    int max1 = INT_MIN, max2 = INT_MIN;
9    int min1 = INT_MAX, min2 = INT_MAX;
10 
11    for (int i = 0; i < n; i++) {
12        // Update Max values
13        if (arr[i] > max1) {
14            max2 = max1;
15            max1 = arr[i];
16        } else if (arr[i] > max2 && arr[i] != max1) {
17            max2 = arr[i];
18        }
19 
20        // Update Min values
21        if (arr[i] < min1) {
22            min2 = min1;
23            min1 = arr[i];
24        } else if (arr[i] < min2 && arr[i] != min1) {
25            min2 = arr[i];
26        }
27    }
28 
29    printf("2nd Largest Element  = %d\n", max2);
30    printf("2nd Smallest Element = %d\n", min2);
31    return 0;
32}

---

Program 2: Merging Two Sorted Arrays into a Third Sorted Array

*Exam Context: Group C (10 Marks)*

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3void mergeSortedArrays(int arr1[], int n1, int arr2[], int n2, int result[]) {
4    int i = 0, j = 0, k = 0;
5 
6    while (i < n1 && j < n2) {
7        if (arr1[i] <= arr2[j]) {
8            result[k++] = arr1[i++];
9        } else {
10            result[k++] = arr2[j++];
11        }
12    }
13 
14    // Copy remaining elements
15    while (i < n1) result[k++] = arr1[i++];
16    while (j < n2) result[k++] = arr2[j++];
17}
18 
19int main() {
20    int arr1[] = {1, 3, 5, 7};
21    int arr2[] = {2, 4, 6, 8, 10};
22    int n1 = 4, n2 = 5;
23    int result[9];
24 
25    mergeSortedArrays(arr1, n1, arr2, n2, result);
26 
27    printf("Merged Sorted Array: ");
28    for (int i = 0; i < 9; i++) {
29        printf("%d ", result[i]);
30    }
31    printf("\n");
32    return 0;
33}

---

Program 3: Adam Number Verification

An Adam Number is a number where the square of the reverse of the number equals the reverse of the square of the number (e.g., 12^2 = 144; reverse of 12 is 21; 21^2 = 441; reverse of 441 is 144).

1"text-[#cf222e] dark:text-[#c586c0] font-semibold">#include "text-[#0a3069] dark:text-[#ce9178]"><stdio.h>
2 
3int reverse(int num) {
4    int rev = 0;
5    while (num > 0) {
6        rev = rev * 10 + (num % 10);
7        num /= 10;
8    }
9    return rev;
10}
11 
12int main() {
13    int num;
14    printf("Enter integer: ");
15    scanf("%d", &num);
16 
17    int sq1 = num * num;
18    int revNum = reverse(num);
19    int sq2 = revNum * revNum;
20 
21    if (sq1 == reverse(sq2))
22        printf("%d is an Adam Number.\n", num);
23    else
24        printf("%d is NOT an Adam Number.\n", num);
25 
26    return 0;
27}

---

6. Key Takeaways for Unit 3

Never return pointers to local automatic stack variables from a function. Local stack memory is deallocated upon function return, resulting in a dangling pointer.
Pass large arrays via pointers (const int *arr) to avoid overhead from copying array elements.

Student Academic Tools

MAKAUT SGPA Calculator

MAKAUT CGPA Calculator

SGPA to Percentage Converter

Percentage to SGPA Converter

CGPA to Percentage Converter

Percentage to CGPA Converter

Internal Marks Calculator

Mid Semester Percentage Calculator

Yearly Percentage Calculator

Grade Calculator

Target SGPA Calculator

Credit Requirement Calculator

Scholarship Eligibility Checker

Streamline your MAKAUT exam preparation today.

MAKAUT C Programming Unit 3: Functions, Storage Classes, Pointers & 1D Arrays Masterclass

1. Modular Programming & Functions

Components of a Function:

2. Storage Classes in C: auto, register, static, extern

3. Parameter Passing: Call by Value vs Call by Reference

Swapping Program: Call by Value vs Call by Reference

4. 1D Array Fundamentals & Pointer-Array Duality

Key Equivalences:

5. Solved High-Scoring MAKAUT Exam Programs

Program 1: Finding 2nd Largest & 2nd Smallest Array Elements (Single Pass O(N))

Program 2: Merging Two Sorted Arrays into a Third Sorted Array

Program 3: Adam Number Verification

6. Key Takeaways for Unit 3

Solved FAQs & Topic Review

Student Academic Tools

MAKAUT SGPA Calculator

MAKAUT CGPA Calculator

SGPA to Percentage Converter

Percentage to SGPA Converter

CGPA to Percentage Converter

Percentage to CGPA Converter

Internal Marks Calculator

Mid Semester Percentage Calculator

Yearly Percentage Calculator

Grade Calculator

Target SGPA Calculator

Credit Requirement Calculator

Scholarship Eligibility Checker

Streamline your MAKAUT exam preparation today.

MAKAUT C Programming Unit 3: Functions, Storage Classes, Pointers & 1D Arrays Masterclass

1. Modular Programming & Functions

Components of a Function:

2. Storage Classes in C: auto, register, static, extern

3. Parameter Passing: Call by Value vs Call by Reference

Swapping Program: Call by Value vs Call by Reference

4. 1D Array Fundamentals & Pointer-Array Duality

Key Equivalences:

5. Solved High-Scoring MAKAUT Exam Programs

Program 1: Finding 2nd Largest & 2nd Smallest Array Elements (Single Pass O(N))

Program 2: Merging Two Sorted Arrays into a Third Sorted Array

Program 3: Adam Number Verification

6. Key Takeaways for Unit 3

Solved FAQs & Topic Review