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C Basics
- WBOYOriginal
- 2024-07-17 11:54:401226browse
C
#include <stdio.h>
int main() {
printf("Hello, World!\n");
return 0;
}
Creating Variables
In C, variables are used to store data that can be manipulated within a program. Here's a comprehensive guide on creating and working with variables in C:
Syntax for Variable Declaration and Initialization
Declaration:
type variable_name;
Example:
int number; char letter; float salary;
Initialization:
variable_name = value;
Example:
number = 10; letter = 'A'; salary = 50000.0;
Declaration and Initialization Combined:
type variable_name = value;
Example:
int age = 25; double pi = 3.14159; char grade = 'A';
Rules for Variable Names
- Variable names must start with a letter (a-z, A-Z) or an underscore (_).
- Subsequent characters can be letters, digits (0-9), or underscores.
- Variable names are case-sensitive (myVar and myvar are different).
- Variable names cannot be C reserved keywords (e.g., int, return, void).
Examples:
int age; char _grade; float salary_2024;
Variable Scope
The scope of a variable is the part of the program where the variable is accessible. Variables in C can be:
Local Variables: Declared inside a function or a block and accessible only within that function or block.
void myFunction() {
int localVar = 5;
printf("%d", localVar);
}
Global Variables: Declared outside of all functions and accessible from any function within the program.
int globalVar = 10;
void myFunction() {
printf("%d", globalVar);
}
int main() {
myFunction(); // Outputs: 10
return 0;
}
Constants
Constants are variables whose values cannot be changed once assigned. They are declared using the const keyword.
Example:
const int DAYS_IN_WEEK = 7; const float PI = 3.14159;
Default Values
In C, uninitialized local variables contain garbage values, while global and static variables are initialized to zero by default.
Example:
#include <stdio.h>
int globalVar; // default value 0
int main() {
int localVar; // contains garbage value
printf("Global Variable: %d\n", globalVar);
printf("Local Variable: %d\n", localVar);
return 0;
}
Declare Many Variables with or without Values
You can declare multiple variables of the same type in a single line, separating them with commas. You can also initialize them either at the time of declaration or later.
Examples:
// Declaring multiple variables without values int a, b, c; // Declaring and initializing some variables int x = 10, y, z = 30;
One Value to Multiple Variables
You can assign the same value to multiple variables by chaining the assignment operator.
Example:
int m, n, o; m = n = o = 50;
Creating Comments
Comments in C are non-executable statements that are used to describe and explain the code. They are essential for making the code more readable and maintainable. C supports two types of comments:
1. Single-Line Comments
Single-line comments start with two forward slashes (//). Everything following // on that line is considered a comment.
Syntax:
// This is a single-line comment int x = 10; // x is initialized to 10
2. Multi-Line Comments
Multi-line comments start with /* and end with */. Everything between /* and */ is considered a comment, regardless of how many lines it spans.
Syntax:
/* This is a multi-line comment. It can span multiple lines. */ int y = 20; /* y is initialized to 20 */
Example Usage
Single-Line Comment Example:
#include <stdio.h>
int main() {
// Print Hello, World!
printf("Hello, World!\n"); // This prints the string to the console
return 0;
}
Multi-Line Comment Example:
#include <stdio.h>
int main() {
/*
This is a simple C program
that prints Hello, World!
to the console.
*/
printf("Hello, World!\n");
return 0;
}
These examples illustrate how to use single-line and multi-line comments in C to make the code more readable and maintainable.
Basic Input and Output in C
In C, input and output operations are performed using standard library functions. The most commonly used functions for basic input and output are printf and scanf.
1. Output using printf
The printf function is used to print text and variables to the console.
Syntax:
printf("format string", variable1, variable2, ...);
Format Specifiers:
- %d or %i - for integers
- %f - for floating-point numbers
- %lf - for double-precision floating-point numbers
- %c - for characters
- %s - for strings
Example:
#include <stdio.h>
int main() {
int age = 25;
float salary = 50000.0;
double pi = 3.141592653589793;
char grade = 'A';
char name[] = "John";
printf("Age: %d\n", age);
printf("Salary: %.2f\n", salary);
printf("Pi: %.15lf\n", pi);
printf("Grade: %c\n", grade);
printf("Name: %s\n", name);
return 0;
}
2. Input using scanf
The scanf function is used to read formatted input from the console.
Syntax:
scanf("format string", &variable1, &variable2, ...);
Example:
#include <stdio.h>
int main() {
int age;
float salary;
double pi;
char grade;
char name[50];
printf("Enter age: ");
scanf("%d", &age);
printf("Enter salary: ");
scanf("%f", &salary);
printf("Enter pi value: ");
scanf("%lf", &pi);
printf("Enter grade: ");
scanf(" %c", &grade); // Note the space before %c to consume any leftover newline character
printf("Enter name: ");
scanf("%s", name); // Reads a single word, stops at whitespace
printf("\nYou entered:\n");
printf("Age: %d\n", age);
printf("Salary: %.2f\n", salary);
printf("Pi: %.15lf\n", pi);
printf("Grade: %c\n", grade);
printf("Name: %s\n", name);
return 0;
}
Important Points
- The & operator is used in scanf to pass the address of the variable where the input will be stored.
- When reading characters with scanf, it's important to handle the newline character left in the input buffer.
- scanf reads strings up to the first whitespace character. For reading a line of text, functions like fgets can be used.
Reading a Line of Text with fgets:
Syntax:
fgets(buffer, size, stdin);
Example:
#include <stdio.h>
int main() {
char name[50];
printf("Enter your full name: ");
fgets(name, sizeof(name), stdin); // Reads a line of text including spaces
printf("Your name is: %s", name);
return 0;
}
Using getchar and putchar for Character Input and Output
getchar Example:
#include <stdio.h>
int main() {
char ch;
printf("Enter a character: ");
ch = getchar();
printf("You entered: ");
putchar(ch);
printf("\n");
return 0;
}
putchar Example:
#include <stdio.h>
int main() {
char ch = 'A';
printf("The character is: ");
putchar(ch);
printf("\n");
return 0;
}
Data Types in C
In C programming, data types specify the type of data that variables can store. C supports several basic and derived data types, each with specific properties. Here's a comprehensive guide to data types in C:
1. Primitive Data Types
Integer Types
- int: Standard integer type, typically 4 bytes.
Example:
int numInt = 100000;
- short: Short integer type, typically 2 bytes.
Example:
short numShort = 1000;
- long: Long integer type, varies by system (commonly 4 or 8 bytes).
Example:
long numLong = 10000000000L;
- long long: Long long integer type, typically 8 bytes (C99 and later).
Example:
long long bigNumber = 123456789012345LL;
Floating-Point Types
- float: Single-precision floating-point, typically 4 bytes.
Example:
float numFloat = 3.14f;
- double: Double-precision floating-point, typically 8 bytes.
Example:
double numDouble = 3.14159;
- long double: Extended precision floating-point, varies by system.
Example:
long double extendedPi = 3.14159265358979323846L;
Character Type
- char: Character type, typically 1 byte. Stores ASCII values (0 to 127) or UTF-8 characters.
Example:
char letter = 'A';
Boolean Type
-
_Bool or bool: Represents true or false values (0 or 1).
- To use boolean type, include
header file.
- To use boolean type, include
Example:
#include <stdbool.h> bool isValid = true;
2. Derived Data Types
Array
- Syntax: type array_name[size];
Example:
int numbers[5] = {1, 2, 3, 4, 5};
Pointer
- Syntax: type *pointer_name;
Example:
int *ptr;
Structure
- Syntax:
struct structure_name {
type member1;
type member2;
// ...
};
Example:
struct Person {
char name[50];
int age;
float salary;
};
Booleans in C
In C, booleans are typically represented using integer types, where 0 represents false and any non-zero value represents true. Let's explore how booleans are handled in C programming:
1. Boolean Representation
In C, there is no dedicated boolean type like in some other languages. Instead, integers (int) are commonly used to represent boolean values.
- _Bool Type: Defined in C standard as a data type capable of holding only 0 (false) or 1 (true).
Example:
#include <stdio.h>
int main() {
_Bool b1 = 1; // true
_Bool b2 = 0; // false
printf("b1: %d\n", b1); // Output: 1 (true)
printf("b2: %d\n", b2); // Output: 0 (false)
return 0;
}
- Using stdbool.h: Introduced in C99, stdbool.h provides a clearer representation with bool, true, and false.
Example:
#include <stdio.h>
#include <stdbool.h>
int main() {
bool isValid = true;
bool isReady = false;
printf("isValid: %d\n", isValid); // Output: 1 (true)
printf("isReady: %d\n", isReady); // Output: 0 (false)
return 0;
}
2. Boolean Evaluation
In C, expressions are evaluated to true (1) or false (0). Here are some examples of expressions and their boolean evaluations:
- Integer and Float Values: Any non-zero integer or non-zero floating-point value is evaluated as true. Zero (0) and zero as float (0.0) are evaluated as false.
Example:
#include <stdio.h>
int main() {
int num = 10;
float salary = 0.0;
if (num) {
printf("num is true\n");
} else {
printf("num is false\n");
}
if (salary) {
printf("salary is true\n");
} else {
printf("salary is false\n");
}
return 0;
}
Output:
num is true salary is false
3. Null Pointer Evaluation
In C, a null pointer is evaluated as false in boolean context. A null pointer is typically represented as (type *)0.
Example:
#include <stdio.h>
int main() {
int *ptr = NULL;
if (ptr) {
printf("ptr is not NULL\n");
} else {
printf("ptr is NULL\n");
}
return 0;
}
Output:
ptr is NULL
Type Casting: Implicit and Explicit
In C programming, type casting refers to converting a value from one data type to another. There are two types of type casting: implicit and explicit. Let's explore each in detail:
1. Implicit Type Casting (Automatic Type Conversion)
Implicit type casting occurs automatically by the compiler when compatible types are mixed in expressions. It promotes smaller data types to larger data types to avoid loss of data. It's also known as automatic type conversion.
Example:
#include <stdio.h>
int main() {
int numInt = 10;
double numDouble = 3.5;
double result = numInt + numDouble; // Implicitly converts numInt to double
printf("Result: %.2lf\n", result); // Output: 13.50
return 0;
}
In this example, numInt (an integer) is implicitly converted to a double before performing the addition with numDouble.
2. Explicit Type Casting (Type Conversion)
Explicit type casting is performed by the programmer using casting operators to convert a value from one data type to another. It allows for precise control over the type conversion process but can lead to data loss if not used carefully.
Syntax:
(type) expression
Example:
#include <stdio.h>
int main() {
double numDouble = 3.5;
int numInt;
numInt = (int)numDouble; // Explicitly casts numDouble to int
printf("numInt: %d\n", numInt); // Output: 3
return 0;
}
In this example, numDouble (a double) is explicitly cast to an int. The decimal part is truncated, resulting in numInt being 3.
Arrays in C
Arrays in C are collections of variables of the same type that are accessed by indexing. They provide a way to store multiple elements under a single name.
1. Declaring Arrays
To declare an array in C, specify the type of elements it will hold and the number of elements enclosed in square brackets [].
Syntax:
type arrayName[arraySize];
- type: Data type of the array elements.
- arrayName: Name of the array.
- arraySize: Number of elements in the array.
Example:
int numbers[5]; // Array of 5 integers
2. Initializing Arrays
Arrays can be initialized either during declaration or after declaration using assignment statements.
Example:
int numbers[5] = {1, 2, 3, 4, 5}; // Initializing during declaration
// Initializing after declaration
int moreNumbers[3];
moreNumbers[0] = 10;
moreNumbers[1] = 20;
moreNumbers[2] = 30;
3. Accessing Array Elements
Array elements are accessed using zero-based indexing, where the first element is at index 0.
Example:
int numbers[5] = {1, 2, 3, 4, 5};
printf("First element: %d\n", numbers[0]); // Output: 1
printf("Second element: %d\n", numbers[1]); // Output: 2
4. Modifying Array Elements
Array elements can be modified by assigning new values to specific indices.
Example:
int numbers[5] = {1, 2, 3, 4, 5};
numbers[2] = 10; // Modify the third element
printf("Modified third element: %d\n", numbers[2]); // Output: 10
5. Multidimensional Arrays
C supports multidimensional arrays, which are arrays of arrays. They are useful for storing tabular data or matrices.
Example:
int matrix[3][3] = {
{1, 2, 3},
{4, 5, 6},
{7, 8, 9}
};
printf("Element at row 2, column 3: %d\n", matrix[1][2]); // Output: 6
6. Passing Arrays to Functions
When passing arrays to functions, C passes them by reference. This means any modifications made to the array within the function affect the original array.
Example:
#include <stdio.h>
void printArray(int arr[], int size) {
for (int i = 0; i < size; i++) {
printf("%d ", arr[i]);
}
printf("\n");
}
int main() {
int numbers[5] = {1, 2, 3, 4, 5};
printArray(numbers, 5); // Pass array and its size to function
return 0;
}
Strings in C
In C programming, strings are arrays of characters terminated by a null ('\0') character. Let's explore how to work with strings, including input, output, and manipulation:
1. Declaring and Initializing Strings
Strings in C are arrays of characters. They can be declared and initialized in several ways:
Syntax:
char strName[size];
Example:
#include <stdio.h>
int main() {
// Declaring and initializing a string
char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};
// Alternatively, using string literal (implicitly adds '\0')
char message[] = "Welcome";
printf("Greeting: %s\n", greeting); // Output: Hello
printf("Message: %s\n", message); // Output: Welcome
return 0;
}
2. String Input with scanf()
To input a string with spaces in C, fgets() from
Example:
#include <stdio.h>
int main() {
char name[50];
printf("Enter your name: ");
fgets(name, sizeof(name), stdin); // Read input including spaces
printf("Hello, %s!\n", name);
return 0;
}
3. String Functions
C provides several library functions for manipulating strings, declared in
- strlen(): Calculates the length of a string.
Example:
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello";
int len = strlen(str);
printf("Length of '%s' is %d\n", str, len); // Output: Length of 'Hello' is 5
return 0;
}
- strcpy(): Copies one string to another.
Example:
#include <stdio.h>
#include <string.h>
int main() {
char src[] = "Hello";
char dest[20];
strcpy(dest, src);
printf("Copied string: %s\n", dest); // Output: Copied string: Hello
return 0;
}
- strcat(): Concatenates two strings.
Example:
#include <stdio.h>
#include <string.h>
int main() {
char str1[20] = "Hello";
char str2[] = " World";
strcat(str1, str2);
printf("Concatenated string: %s\n", str1); // Output: Concatenated string: Hello World
return 0;
}
- strcmp(): Compares two strings.
Example:
#include <stdio.h>
#include <string.h>
int main() {
char str1[] = "Hello";
char str2[] = "Hello";
if (strcmp(str1, str2) == 0) {
printf("Strings are equal\n");
} else {
printf("Strings are not equal\n");
}
return 0;
}
4. Handling String Input Safely
When using fgets() for string input, ensure buffer overflow doesn't occur by specifying the maximum length of input to read.
Example:
#include <stdio.h>
int main() {
char sentence[100];
printf("Enter a sentence: ");
fgets(sentence, sizeof(sentence), stdin); // Read up to 99 characters plus '\0'
printf("You entered: %s\n", sentence);
return 0;
}
5. Null-Terminated Strings
C strings are null-terminated, meaning they end with a null character '\0'. This character indicates the end of the string and is automatically added when using string literals.
Example:
#include <stdio.h>
int main() {
char message[] = "Hello"; // Automatically includes '\0'
// Printing characters until '\0' is encountered
for (int i = 0; message[i] != '\0'; ++i) {
printf("%c ", message[i]);
}
printf("\n");
return 0;
}
Operators in C
Operators in C are symbols used to perform operations on variables and values. They are categorized into several types based on their functionality.
Arithmetic Operators
Arithmetic operators are used for basic mathematical operations.
| Operator | Name | Description | Example |
|---|---|---|---|
| + | Addition | Adds two operands | x + y |
| - | Subtraction | Subtracts the right operand from the left | x - y |
| * | Multiplication | Multiplies two operands | x * y |
| / | Division | Divides the left operand by the right operand | x / y |
| % | Modulus | Returns the remainder of the division | x % y |
| ++ | Increment | Increases the value of operand by 1 | x++ or ++x |
| -- | Decrement | Decreases the value of operand by 1 | x-- or --x |
#include <stdio.h>
int main() {
int a = 10, b = 3;
printf("a + b = %d\n", a + b); // Output: 13
printf("a / b = %d\n", a / b); // Output: 3
printf("a %% b = %d\n", a % b); // Output: 1 (Modulus operation)
int x = 5;
x++;
printf("x++ = %d\n", x); // Output: 6
int y = 8;
y--;
printf("y-- = %d\n", y); // Output: 7
return 0;
}
Assignment Operators
Assignment operators are used to assign values to variables and perform operations.
| Operator | Name | Description | Example |
|---|---|---|---|
| = | Assignment | Assigns the value on the right to the variable on the left | x = 5 |
| += | Addition | Adds right operand to the left operand and assigns the result to the left | x += 3 |
| -= | Subtraction | Subtracts right operand from the left operand and assigns the result to the left | x -= 3 |
| *= | Multiplication | Multiplies right operand with the left operand and assigns the result to the left | x *= 3 |
| /= | Division | Divides left operand by right operand and assigns the result to the left | x /= 3 |
| %= | Modulus | Computes modulus of left operand with right operand and assigns the result to the left | x %= 3 |
#include <stdio.h>
int main() {
int x = 10;
x += 5;
printf("x += 5: %d\n", x); // Output: 15
return 0;
}
Comparison Operators
Comparison operators are used to compare values.
| Operator | Name | Description | Example |
|---|---|---|---|
| == | Equal | Checks if two operands are equal | x == y |
| != | Not Equal | Checks if two operands are not equal | x != y |
| > | Greater Than | Checks if left operand is greater than right | x > y |
| < | Less Than | Checks if left operand is less than right | x < y |
| >= | Greater Than or Equal | Checks if left operand is greater than or equal to right | x >= y |
| <= | Less Than or Equal | Checks if left operand is less than or equal to right | x <= y |
#include <stdio.h>
int main() {
int a = 5, b = 10;
printf("a == b: %d\n", a == b); // Output: 0 (false)
printf("a < b: %d\n", a < b); // Output: 1 (true)
return 0;
}
Logical Operators
Logical operators combine Boolean expressions.
| Operator | Description | Example |
|---|---|---|
| && | Logical AND | x < 5 && x < 10 |
| || | Logical OR | x < 5 || x < 4 |
| ! | Logical NOT | !(x < 5 && x < 10) |
#include <stdio.h>
int main() {
int x = 3;
printf("x < 5 && x < 10: %d\n", x < 5 && x < 10); // Output: 1 (true)
printf("x < 5 || x < 2: %d\n", x < 5 || x < 2); // Output: 1 (true)
return 0;
}
Bitwise Operators
Bitwise operators perform operations on bits of integers.
| Operator | Name | Description | Example |
|---|---|---|---|
| & | AND | Sets each bit to 1 if both bits are 1 | x & y |
| | | OR | Sets each bit to 1 if one of two bits is 1 | x | y |
| ^ | XOR | Sets each bit to 1 if only one of two bits is 1 | x ^ y |
| ~ | NOT | Inverts all the bits | ~x |
| << | Left Shift | Shifts bits to the left | x << 2 |
| >> | Right Shift | Shifts bits to the right | x >> 2 |