L&T Technology Services C Programming with DSA Interview Questions & Answers
Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About L&T Technology Services hiring for C Programming with DSA roles
L&T Technology Services is an engineering research and development services company and part of the Larsen & Toubro group. It works with clients in transportation, industrial products, telecom, medical devices and plant engineering on product design, embedded systems and digital engineering. In India it hires engineers for software, embedded, testing and data roles across its engineering and delivery centres.
For C Programming with DSA roles, this L&T Technology Services practice set focuses most on Arrays and Strings (6), C Basics, Data Types and Operators (4), Pointers and Memory Management (4), Stacks, Queues and Hashing (4). It has 15 easy, 15 medium questions, so you can start easy and work up to the harder ones.
Company type
IT services
Headquarters
Vadodara, India
Main India offices
Vadodara, Bengaluru, Chennai, Mysuru, Pune
L&T Technology Services C Programming with DSA interview process
Online assessment (aptitude + technical MCQs)
Technical interview
Managerial round
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
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01
What is the difference between break and continue in C?
break immediately exits the nearest enclosing loop or switch statement, and execution continues after it. continue skips the rest of the current loop iteration and moves to the next one; in a for loop the update expression still runs. In nested loops both affect only the innermost loop, so a flag or goto is needed to exit outer loops early.
A double pointer, such as int **pp, stores the address of a pointer. It is needed when a function must change the caller's pointer itself, for example inserting at the head of a linked list or allocating memory inside a function and returning it through a parameter. It is also used for dynamic 2D arrays and arrays of strings, like char **argv.
03
How do you pass a structure to a function efficiently?
Passing a struct by value copies every member, which is costly for large structs. Pass a pointer instead, and add const when the function should only read it, such as void print(const Student *s). Access members with s->name. Small structs of a few bytes can be passed by value safely, and returning small structs by value is also fine.
04
What is the difference between an array and a pointer?
An array is a block of contiguous elements whose size is fixed and known to the compiler; sizeof gives the full array size. A pointer is a variable holding an address; sizeof gives the pointer size. An array name decays to a pointer to its first element in most expressions, but it cannot be reassigned. When passed to a function, an array always becomes a pointer, losing its length.
Quicksort is O(n log n) on average and very fast in practice with in-place partitioning, but O(n squared) in the worst case with poor pivots and not stable. Merge sort is always O(n log n) and stable but needs O(n) extra memory. Heap sort is O(n log n) worst case and in place but not stable and slower due to poor cache use. C's qsort is usually a tuned hybrid.
06
What does sizeof return for a pointer and for an array?
sizeof on a pointer returns the size of the pointer itself, typically 8 bytes on a 64-bit system, regardless of what it points to. sizeof on an array declared in the same scope returns the total bytes of all elements, so sizeof arr / sizeof arr[0] gives the element count. Inside a function receiving an array parameter, sizeof returns pointer size, so pass the length separately.
A prefix sum array stores pre[i] = sum of elements from index 0 to i-1. Then the sum of any range from l to r is pre[r + 1] - pre[l] in O(1) after O(n) preprocessing. It is used for range sum queries, counting subarrays with a given sum together with a hash map, and 2D versions for matrix region sums.
A pointer is a variable that stores the memory address of another variable. int *p = &x; makes p hold the address of x, and *p reads or writes the value at that address. Pointers allow passing large data efficiently, modifying caller variables, working with arrays and strings, building dynamic data structures like linked lists and allocating memory at runtime.
09
A program reads a file with while (!feof(fp)) and processes the last line twice. Why?
feof() becomes true only after a read has already failed at end of file. The loop checks feof before reading, so the final failed read leaves the old buffer content, which is processed again. Loop on the read function's return value instead, such as while (fgets(line, sizeof line, fp) != NULL), and check ferror after the loop.
10
What is a heap and how does it implement a priority queue?
A binary heap is a complete binary tree stored in an array where every parent is smaller than its children for a min heap, or larger for a max heap. For index i, children are at 2i + 1 and 2i + 2. Insert adds at the end and sifts up, and extracting the top swaps it with the last element and sifts down, both O(log n). Building a heap from an array takes O(n).
A stack is a last in, first out structure with push, pop and peek operations, all O(1). It is used for function call frames, undo features, expression evaluation, balanced bracket checking, backtracking and depth first search. In C you implement it with an array and a top index, or with a linked list when the size is not known in advance.
12
A function to insert at the head does not change the list in main. Why?
C passes arguments by value, so the function receives a copy of the head pointer; changing that copy does not affect main. Pass a pointer to the head, as in void push(Node **head, int x), and assign *head = newNode, or return the new head and assign it in the caller with head = push(head, x). This is a very common fresher interview mistake.
13
How would you detect if two linked lists intersect and find the intersection node?
Two lists intersect if they share a node by address, not just value. Compute both lengths, advance the longer list by the difference, then move both together until the pointers are equal. A neat trick is to walk pointer a through list A then B, and pointer b through B then A; they meet at the intersection or both reach NULL. Both are O(m + n) time and O(1) space.
14
Why is gets() dangerous and what should you use instead?
gets() reads a line into a buffer without knowing its size, so long input overflows the buffer and can be used for code execution attacks. It was removed in C11. Use fgets(buf, sizeof buf, stdin), which stops at the buffer size and keeps the newline, then strip the newline if needed. For formatted input, give scanf field widths like %19s.
15
How do you check whether a linked list is a palindrome in O(1) extra space?
Find the middle with slow and fast pointers, reverse the second half in place, then compare the first half and the reversed second half node by node. Finally reverse the second half again to restore the list, which interviewers appreciate. Time is O(n) and extra space is O(1). A simpler O(n) space approach copies values into an array or stack first.
Track the best sum ending here and the overall best.
long maxSubarray(const int *a, int n) {
long cur = a[0], best = a[0];
for (int i = 1; i < n; i++) {
cur = (cur + a[i] > a[i]) ? cur + a[i] : a[i];
if (cur > best) best = cur;
}
return best;
}
Input {-2, 1, -3, 4, -1, 2, 1, -5, 4} returns 6 for subarray 4, -1, 2, 1.
17
What is the two-pointer technique and when is it used?
Two pointers keep two indexes that move through an array according to a rule, often from both ends of a sorted array or at different speeds. It solves pair sum on sorted arrays, removing duplicates in place, reversing, merging sorted arrays and partitioning. It usually gives O(n) time and O(1) extra space instead of nested loops.
18
What does the static keyword do in different contexts?
Inside a function, a static local variable keeps its value between calls and is initialised only once. At file level, a static global variable or function has internal linkage, so it is visible only in that source file, which helps hide implementation details. Static variables are stored in the data or BSS segment, not the stack, and default to zero.
Big O describes how an algorithm's time or memory grows as input size grows, ignoring constants and lower terms. Common classes are O(1), O(log n), O(n), O(n log n), O(n squared) and O(2 to the n). It usually describes the worst case. For example, binary search is O(log n), so a million elements need about 20 steps. Big Omega and Big Theta describe lower and tight bounds.
In-order visits left, node, right and gives sorted output for a BST. Pre-order visits node, left, right and is used to copy or serialise a tree. Post-order visits left, right, node and is used to delete a tree or evaluate expression trees. Level-order visits nodes level by level using a queue. The first three are depth first and use recursion or an explicit stack.
21
Write a header guard and explain why it is needed.
A header guard stops a header from being included twice in one translation unit, which would cause redefinition errors.
#ifndef MATH_UTILS_H
#define MATH_UTILS_H
int add(int a, int b);
#endif
Most compilers also support #pragma once, which is shorter but not part of the C standard.
Flip each next pointer while walking the list.
typedef struct Node { int data; struct Node *next; } Node;
Node *reverse(Node *head) {
Node *prev = NULL, *cur = head;
while (cur) {
Node *next = cur->next;
cur->next = prev;
prev = cur;
cur = next;
}
return prev;
}
Time O(n), space O(1). The returned prev is the new head.
Sliding window solves problems on contiguous subarrays or substrings by keeping a window with two indexes and moving them forward instead of rechecking every subarray. A fixed window finds things like the maximum sum of k elements, while a variable window expands and shrinks, as in the longest substring without repeating characters. It turns O(n squared) brute force into O(n).
24
A search on a sorted array of 10 lakh elements is done with a linear loop. How would you justify changing it?
Linear search takes up to 10 lakh comparisons, while binary search needs about 20, because log base 2 of 10 lakh is roughly 20. If searches are frequent, this is a huge saving at zero memory cost. If data changes often, keeping it sorted costs inserts, so consider a balanced tree or hash table. Measure with realistic workloads before and after.
25
Two source files both define a global variable named count and the build fails. How do you fix it?
Each global may be defined only once. Define it in one .c file, such as int count = 0;, and declare it in a shared header as extern int count;, which other files include. If the variable should be private to each file, mark it static in both files instead. Since GCC 10, -fno-common is default, so duplicate tentative definitions also fail to link.
26
What is the difference between char s[] = "hello" and char *s = "hello"?
char s[] = "hello" creates a modifiable array of 6 bytes, usually on the stack, initialised with a copy of the literal. char *s = "hello" makes a pointer to a string literal stored in read-only memory; modifying it is undefined behaviour and often crashes. Declare such pointers as const char * so the compiler catches accidental writes.
27
What is a deque and how can it be implemented in C?
A deque, or double ended queue, supports insertion and removal at both the front and the rear in O(1). In C it is commonly implemented as a circular array with front and rear indexes that wrap using modulo, or as a doubly linked list. It is the core of the sliding window maximum algorithm and can act as both a stack and a queue.
28
Why are self-balancing trees like AVL and red-black trees needed?
A plain BST can degrade to a linked list with O(n) operations when data arrives in sorted order. AVL trees keep the height difference of subtrees at most one using rotations, giving faster lookups. Red-black trees use colour rules with looser balance, so inserts and deletes need fewer rotations. Both guarantee O(log n). Red-black trees are used in the Linux kernel, C++ std::map and Java TreeMap.
29
What is structure padding and how can you reduce it?
The compiler inserts padding bytes between members so each one is aligned, which can make a struct larger than the sum of its members. struct { char a; int b; char c; } is usually 12 bytes instead of 6. Reduce padding by ordering members from largest to smallest alignment. Packing with __attribute__((packed)) removes padding but can slow access or fault on some CPUs.
30
Implement a circular queue with enqueue and dequeue in C.
Use modulo arithmetic and a count.
#define CAP 8
typedef struct { int a[CAP]; int front, rear, count; } Queue;
int enqueue(Queue *q, int x) {
if (q->count == CAP) return -1;
q->a[q->rear] = x;
q->rear = (q->rear + 1) % CAP;
q->count++;
return 0;
}
int dequeue(Queue *q, int *x) {
if (q->count == 0) return -1;
*x = q->a[q->front];
q->front = (q->front + 1) % CAP;
q->count--;
return 0;
}
Tips to crack the L&T Technology Services C Programming with DSA interview
Revise core engineering subjects from your branch along with C, basic data structures and one scripting language before the technical round.
Be ready to explain an academic or internship project end to end, including design choices, tools used and testing approach.
Read about LTTS segments like mobility, medical devices and plant engineering so you can connect your skills to a domain.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; L&T Technology Services interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the L&T Technology Services C Programming with DSA interview?
Candidates usually go through 4 stages: Online assessment (aptitude + technical MCQs); Technical interview; Managerial round; HR round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the L&T Technology Services C Programming with DSA interview?
This practice set leans on Arrays and Strings (6), C Basics, Data Types and Operators (4), Pointers and Memory Management (4), Stacks, Queues and Hashing (4). Revise those first, then practise explaining one or two of your own projects end to end, because most L&T Technology Services interviewers ask you to walk through real work.
Are these the exact questions asked at L&T Technology Services?
No. These are curated practice questions that match the skills and difficulty usually tested in it services interviews like L&T Technology Services's. They are not a leaked or verified list of past questions.
Where does L&T Technology Services hire C Programming with DSA professionals in India?
L&T Technology Services has large teams in Vadodara, Bengaluru, Chennai, Mysuru, Pune. Openings and locations change often, so check the L&T Technology Services careers page and filter by city and experience.
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