C questions in placement tests and university exams are rarely about syntax alone. Most of what you will find here is output prediction, pointer arithmetic, arrays and strings, structures and unions, storage classes, recursion, and file handling. The explanations walk through memory behaviour step by step, which is usually where the confusion sits rather than in the code itself.
What will be the output of the following code? char str[] = "Code"; printf("%c", str[2]);
Answer: C
String "Code" has indices: C(0), o(1), d(2), e(3). str[2] refers to 'd'.
Q.2Medium
What is the difference between char str[] = "Test" and char *str = "Test"?
Answer: B
char[] creates a modifiable array with its own storage. char* points to read-only string literal in memory.
Q.3Medium
Which function is used to reverse a string in C library?
Answer: C
There is no standard library function for string reversal. strrev() is non-standard (available in some compilers). Manual reversal or custom functions are needed.
Q.4Medium
What is the output of the following code? int arr[] = {10, 20, 30}; printf("%d", sizeof(arr)/sizeof(arr[0]));
Answer: C
sizeof(arr) gives total bytes of array. sizeof(arr[0]) gives bytes of one element. Division gives number of elements: 3.
Q.5Medium
What will be printed by: printf("%s", "Hello\0World");?
Answer: B
\0 is the null terminator which marks the end of a string. %s stops printing at the first null character.
Q.6Medium
Consider: int *ptr = arr; where arr is an array. What does ptr[2] represent?
Answer: B
ptr[2] is equivalent to *(ptr+2), which points to the third element (index 2) of the array.
Q.7Medium
What will the following code output? char str[20]; strcpy(str, "Competitive"); strcat(str, " Exam"); printf("%s", str);
Answer: C
strcpy copies "Competitive" to str. strcat appends " Exam" to it, resulting in "Competitive Exam".
Q.8Medium
What is the time complexity of searching for an element in an unsorted array of size n?
Answer: C
Linear search on unsorted array requires checking each element in worst case, giving O(n) time complexity.
Q.9Medium
What will be the output of this code? int arr[5]; for(int i=0; i<5; i++) arr[i] = i*i; printf("%d %d %d", arr[1], arr[2], arr[4]);
Which of the following correctly declares and initializes a 2D array?
Answer: C
Both syntax forms are valid in C. Elements can be provided in nested braces or as a linear list, and they fill row by row.
Q.11Medium
What is the relationship between array name and pointer in C?
Answer: A
Array names decay to pointers to the first element in expressions, but they are not truly pointer variables. The array name cannot be reassigned.
Q.12Medium
If str = "Hello", what is the value of str[5]?
Answer: A
"Hello" has 5 characters, so valid indices are 0-4. Index 5 contains the null terminator '\0' that marks the end of the string.
Q.13Medium
In a 2D array int matrix[4][5], which statement about memory layout is true?
Answer: A
C uses row-major order for 2D arrays. matrix[0][0], matrix[0][1]...matrix[0][4], matrix[1][0]... are stored sequentially in memory.
Q.14Medium
What is the output of sizeof(arr)/sizeof(arr[0]) when arr is declared as int arr[10]?
Answer: A
This expression calculates array length. sizeof(arr) gives total bytes (40 on 32-bit system), sizeof(arr[0]) gives bytes per element (4), so 440=10.
Q.15Medium
Which string function modifies the original string in-place?
Answer: D
Both strtok() (modifies by replacing delimiters with '\0') and strcpy() (copies and overwrites destination) modify strings in-place.
Q.16Medium
What happens when you try to modify a string literal in C?
Answer: C
String literals are stored in read-only memory. Attempting modification causes undefined behavior (often segmentation fault). This is why char *str = "text"; str[0]='T'; is dangerous.
Q.17Medium
What is the time complexity of inserting an element at the beginning of an unsorted array?
Answer: B
Inserting at the beginning requires shifting all n elements one position right, making it O(n). Insertion at the end is O(1) if space exists.
Q.18Medium
Which function is used to find the first occurrence of a character in a string?
Answer: B
strchr() finds the first occurrence of a character. strrchr() finds the last occurrence. strstr() finds substrings.
Q.19Medium
What will be the output? char arr[] = "ABC"; printf("%d", sizeof(arr));
Answer: B
sizeof includes the null terminator. "ABC" has 4 bytes (A, B, C, \0).
Q.20Medium
Consider the code: int *p; int arr[5] = {10, 20, 30, 40, 50}; p = arr; What is *(p+2)?
Answer: B
p points to arr[0]. p+2 points to arr[2], which contains 30.
