C Language Interview Questions: Analysis of High-Frequency Issues Related to Pointers and Arrays

In C language, pointers and arrays are two extremely important and closely related concepts. In interviews, these two are often asked together, especially regarding how to use them, their differences, and how to apply them correctly. Next, we will explore these two topics through several common questions.

1. Basic Concepts of Pointers and Arrays

1.1 Arrays

An array is a data structure consisting of elements of the same type, with a size fixed at creation. For example, an integer array can be declared as follows:

int arr[5]; // Declare an array containing 5 integers

This code allocates space for a block of memory that can store five integers. We can access these elements by index, such as <span>arr[0]</span>, <span>arr[1]</span>, etc.

1.2 Pointers

A pointer is a special type of variable used to store the address of other variables (e.g., function parameters, data structures). For example:

int *ptr; // Declare an integer pointer

Here, <span>ptr</span> is an integer pointer but has not yet pointed to any valid address; it can be assigned to point to a specific variable.

2. Relationship Between Pointers and Arrays

The name of an array actually represents the address of the first element in that array, so it can be seen as a special type of pointer. For example:

int arr[5] = {10, 20, 30, 40, 50}; int *ptr = arr; // ptr now holds the address of arr[0]

Note: In many cases, <span>arr</span> and <span>&arr[0]</span> can be used interchangeably, but it is important to distinguish between the “whole array” and “individual elements”.

3. Examples of High-Frequency Interview Questions and Answers

Question 1: Compare performance between printing an array and using a pointer

Write a program to demonstrate how to use an array and a pointer by passing them to a function to capture the corresponding values and output the results, showing the performance differences between the two.

#include <stdio.h>
void printArray(int arr[], int size) {    for (int i = 0; i < size; i++) {        printf("%d ", arr[i]);    }    printf("\n");}
void printPointer(int *ptr, int size) {    for (int i = 0; i < size; i++) {        printf("%d ", *(ptr + i));    }   printf("\n");}
int main() {    int numbers[] = {10, 20, 30, 40, 50};        printf("Using Array:\n");    printArray(numbers, sizeof(numbers)/sizeof(numbers[0]));        printf("Using Pointer:\n");    printPointer(numbers, sizeof(numbers)/sizeof(numbers[0]));
   return 0;}

Output:

Using Array:10 20 30 40 50 Using Pointer:10 20 30 40 50

In the above example, regardless of whether the function is passed an array with multiple elements or a pointer, both forms can access the data. However, the latter is generally recommended for closer performance. This method also positively impacts safety against null pointer dereferencing, thus avoiding unnecessary out-of-bounds errors. Additionally, it may introduce methods to enhance the handling of complex data, reflecting the required flexibility, increasing safety, improving efficiency, and expanding functionality. Therefore, choosing the appropriate format based on needs can lead to thorough discussions on which mode is most reasonable, depending on the scenario and specific requirements.

Question 2: Explain what the following code outputs and why

Consider the following code segment:

#include <stdio.h>
void updateValue(int* ptr) {    *ptr += (*ptr);}
int main() {     int value =10;     updateValue(&value);     printf("%d\n", value);           return(0);}

Output:

20

Analysis:

• In the main function, the address of <span>value</span> is passed to the <span>updateValue()</span> function.
• Inside the function, the content in the original memory area is modified using the dereference operator (<span>*</span>), so the updated value becomes double the original.

This method is very convenient, allowing direct manipulation of the original data, enhancing the ability to dynamically modify components and avoiding redundant assignments that cause unnecessary computations (improving business efficiency).

Conclusion

Mastering pointers and arrays in C language is crucial for programming. It is important not only to understand the significant relationship between the two but also to be adept at using them to solve practical problems. I hope this article helps everyone approach related questions in C language interviews with more confidence. If you have any other questions or want to learn more, please continue to explore.