Johnson Lin

Redis, an open-source, in-memory data structure store, offers a wide range of commands to manipulate data structures like strings, lists, sets, hashes, bitmaps, hyperloglogs, and more. Among these, the HyperLogLog data type is particularly useful for approximating the number of unique elements in a set when the set is too large to fit into memory or when you don’t need absolute accuracy. The PFADD command is one of the key operations for working with HyperLogLog in Redis. This guide will...

In the ever-evolving world of technology, understanding the fundamentals of data structures and algorithms is not just an option but a necessity. These concepts form the backbone of efficient problem-solving and lie at the heart of many computer science disciplines, from software development to data analytics. Here’s why every aspiring tech professional should prioritize learning data structures and algorithms. Efficiency and Optimization:Data structures and algorithms determine how...

Type and Macros in math.hThe math.h header defines two type aliases: float_t: The type that provides the most efficient execution of float operations on the current system, with a width that is at least equal to that of a float. double_t: The type that provides the most efficient execution of double operations on the current system, with a width that is at least equal to that of a double. You can determine their specific types using the FLT_EVAL_METHOD macro. Mapping of FLT_EVAL_METHOD...

OverviewThe locale.h header file manages localization settings in programs, affecting the following behaviors: Number formatting Currency formatting Character classification Date and time formatting It defines several macros: LC_COLLATE: Influences string comparison functions strcoll() and strxfrm(). LC_CTYPE: Affects character processing functions. LC_MONETARY: Impacts currency formatting. LC_NUMERIC: Modifies number formatting for printf(). LC_TIME: Affects date and time formatting...

The limits.h header provides macros that define the range of values for various integer types, including character types. Here are the key macros: CHAR_BIT: Number of bits in a character. SCHAR_MIN: Minimum value of a signed char. SCHAR_MAX: Maximum value of a signed char. UCHAR_MAX: Maximum value of an unsigned char. CHAR_MIN: Minimum value of a char. CHAR_MAX: Maximum value of a char. MB_LEN_MAX: Maximum number of bytes in a multibyte character. SHRT_MIN: Minimum value of a short...

The iso646.h header file specifies alternative spellings for some common operators. For example, it uses the keyword and as a substitute for the logical operator &&. Here’s how the following condition can be expressed using these alternatives: 123if (x > 6 and x < 12)// is equivalent toif (x > 6 && x < 12) The defined alternative spellings are as follows: and replaces && and_eq replaces &= bitand replaces & bitor replaces | compl replaces ~ not...

In C, the inttypes.h header file provides format specifiers for integer types defined in stdint.h that can be used with printf() and scanf(). Here are the four types of integer types available: Fixed-width integer types, e.g., int8_t Minimum-width integer types, e.g., int_least8_t Fastest minimum-width integer types, e.g., int_fast8_t Maximum-width integer types, e.g., intmax_t The format specifiers for printf() are formed by combining PRI + original specifier + type keyword/width. For...

The header file float.h defines various macros related to the floating-point types float, double, and long double, specifying their ranges and precision. FLT_ROUNDSThis macro indicates the rounding direction used in floating-point addition. Its possible values are: -1: Undetermined. 0: Round towards zero. 1: Round to the nearest integer. 2: Round towards positive infinity. 3: Round towards negative infinity. FLT_RADIXThis macro represents the base of the exponent in scientific notation,...

The errno VariableThe errno.h header file declares the errno variable, which is an int used to store error codes (positive integers). If errno has a non-zero value, it indicates that an error occurred during the execution of a program. 123456789int x = -1;errno = 0; // Reset errno to 0int y = sqrt(x); // Attempt to calculate the square root of a negative numberif (errno != 0) { fprintf(stderr, "sqrt error; program terminated.\n"); exit(EXIT_FAILURE);} In this...

The <ctype.h> header file defines a set of prototypes for character handling functions. Character Testing FunctionsThese functions are used to determine whether a character belongs to a specific type: isalnum(): Checks if the character is alphanumeric. isalpha(): Checks if the character is a letter. isdigit(): Checks if the character is a digit. isxdigit(): Checks if the character is a hexadecimal digit. islower(): Checks if the character is a lowercase letter. isupper(): Checks if...

assert()The assert.h header file defines the assert() macro, which is used to verify that a program meets certain conditions at runtime. If a condition is not met, the program will terminate with an error message. This macro is often referred to as an “assertion.” For example, consider the following code: 1assert(PI > 3); When the program reaches this line, it checks whether the variable PI is greater than 3. If it is, the program continues to run; if not, the program will terminate and...

Overview of UnicodeWhen the C language was first developed, it primarily focused on English characters, utilizing 7-bit ASCII to represent all characters. The ASCII range spans from 0 to 127, which means it can represent a maximum of about 128 characters, with each character fitting into a single byte. However, dealing with non-English characters requires more than one byte. For example, just the Chinese language includes tens of thousands of characters, necessitating a character set that...

Command Line ArgumentsC programs can receive parameters from the command line. For example, running: 1$ ./foo hello world The program foo receives two command line arguments: hello and world. How does the program access these command line arguments? C stores the command line input in an array, which can be accessed through the parameters of the main() function. 1234567#include <stdio.h>int main(int argc, char* argv[]) { for (int i = 0; i < argc; i++) { ...

When a data type has only a few possible values, each with its own specific meaning, defining these values as an enum (short for “enumeration”) can enhance code readability. 12345enum colors { RED, GREEN, BLUE };printf("%d\n", RED); // 0printf("%d\n", GREEN); // 1printf("%d\n", BLUE); // 2 In the example above, if a program requires three colors, we can use the enum command to define these colors as a single enumeration type called colors, which...

Sometimes, you need a data structure that can represent different data types depending on the situation. For instance, if you use a single structure to represent the quantity of fruit, it may need to be an integer (like 6 apples) at times and a float (like 1.5 kilograms of strawberries) at others. In C, you can use a union to create a flexible data structure. A union can contain various members that share the same memory space, meaning only one member can hold a meaningful value at any given...

OverviewThe typedef command is used to create an alias for a specific type. 1typedef type name; In this code, type represents the original type, while name is the alias. For example: 1typedef unsigned char BYTE; In this example, typedef creates an alias BYTE for the type unsigned char, allowing you to declare variables using BYTE: 1BYTE c = 'z'; Multiple AliasesYou can use typedef to define multiple aliases at once: 1typedef int antelope, bagel, mushroom; Here, antelope, bagel, and...

OverviewC doesn’t have a dedicated string type. Instead, strings are treated as arrays of characters (char arrays). For example, the string “Hello” is processed as the array {‘H’, ‘e’, ‘l’, ‘l’, ‘o’}. The compiler allocates a continuous block of memory for the array, with all characters stored in adjacent memory units. C automatically adds a null byte (‘\0’) at the end of the string to indicate its termination. This null character is different from the character ‘0’. The null character has...

IntroductionAn array is a collection of values of the same type stored in a sequential manner. Arrays are represented by a variable name followed by square brackets, with the number inside the brackets indicating the number of elements in the array. 1int scores[100]; In this example, an array named scores is declared with 100 elements, each of which is of type int. Note: When declaring an array, you must specify its size. Array elements are indexed starting from 0. Thus, in an array...

OverviewA function is a reusable block of code that can accept different parameters and perform specific tasks. Here’s an example of a function: 123int plus_one(int n) { return n + 1;} This code declares a function named plus_one(). Key Points of Function Declarations: Return Type: Specify the return type at the start of the declaration. In the example, int indicates the function returns an integer. Parameters: Declare the types and names of parameters in parentheses following...

Pointers are one of the most important and challenging concepts in the C programming language. OverviewWhat is a pointer? In essence, it’s a value representing a memory address, acting as a signpost to a specific location in memory. The asterisk * represents a pointer and is usually placed after the type keyword to indicate what type of value the pointer is referencing. For example, char* is a pointer to a character, and float* is a pointer to a float. 1int* intPtr; The above example...