Datatypes
#include <stdio.h>
// struct datatype
struct Person {
char name[50];
int age;
float salary;
};
// enum datatype
enum color {RED, GREEN, BLUE};
int main() {
// Basic data types
int a = 10; // 4 bytes
float b = 5.5; //4 bytes
char c = 'A'; //1 byte
double d = 2.3; //8 bytes
long double e; // 16 bytes (64-bit), 12 bytes (32-bit)
short integer f; // 2 bytes
long int g; //8 bytes (64-bit), 4 bytes (32-bit)
// Array
int arr[5] = {1, 2, 3, 4, 5};
// Pointer
int *ptr = &a;
// Structure
struct Person person1;
person1.age = 30;
person1.salary = 55000.50;
// Enumeration
enum color myColor = RED;
// Print values
printf("Integer: %d\n", a);
printf("Float: %.2f\n", b);
printf("Character: %c\n", c);
printf("Array: %d\n", arr[0]);
printf("Pointer: %d\n", *ptr);
printf("Structure: Name = %s", person1.name);
printf("Enumeration: %d\n", myColor);
return 0;
}
Real data type:
float,double and long double
Segments of memory
Text Segment (Code Segment)
It contains the compiled machine codeData Segment
Stores global and static variables that are initialized by the programmer.
Two types:
Initialized Data Segment: Contains global and static variables that are explicitly initialized in the program.
Ex. int x=2;
Uninitialized Data Segment (BSS): Contains global and static variables that are not explicitly initialized.
Ex. int x;
Heap
It is used for dynamic memory allocation during runtime.Stack
It stores local variables, function parameters, and return addresses.
Function Prototype
It is a declaration of a function that specifies the function's name, return type, and parameters, but does not provide the function body.
(Note: It is placed at the beginning of the source file and this can be many but only one definition)
#include <stdio.h>
// Function prototype with formal parameters
void func(char name[]);
int main() {
char name[] = "Alice";
//actual parameters
greet(name);
return 0;
}
// Function definition
void func(char name[]) {
printf("Hello, %s!\n", name);
}
MOD/modulus
This operator is used on only integer datatype. It is illegal to use modulus on float datatype
#include <stdio.h>
#include <math.h>
int main() {
double dividend = 7.5;
double divisor = 2.0;
double result;
int i=2;
i=i%10;//works on integer types
result = fmod(dividend, divisor);
printf("%.1f",result); //for float types
return 0;
}
For loop
#include<stdio.h>
int main()
{
int x;
for(x=1; x<=10; x++)
{
// Ternary conditional operator
a <= 20 ? (b = 30) : (c = 30);
}
return 0;
}
While Loop
#include<stdio.h>
int main()
{
int j=1;
while(j <= 255)
{
j++;
}
return 0;
}
MACRO
It is a fragment of code that is given a name and can be used to perform text substitution in the code during the preprocessing phase before actual compilation.
#define PI 3.14159
#define SQUARE(x) ((x) * (x))
Switch case
#include <stdio.h>
int main() {
int day = 3;
switch (day) {
case 1:
printf("Monday\n");
break;
case 2:
printf("Tuesday\n");
break;
default:
printf("Invalid day\n");
break;
}
return 0;
}
Memory Management
Malloc: Allocates memory but does not initialize it. The memory contains garbage values.
Calloc: Allocates memory and initializes all bits to zero.
#include <stdio.h>
#include <stdlib.h>
int main() {
int *array;
int size = 5;
// Allocate memory for an array of integers
array = (int *)malloc(size * sizeof(int));
// Deallocate the memory
free(array);
int *a[3];
a = (int*) malloc(sizeof(int)*3);
free(a);
return 0;
}
Pointers
It provides a way to directly access and manipulate memory.
A pointer is a variable that stores the memory address of another variable. Instead of holding a data value directly, a pointer holds the location of the data in memory.
Basic Pointer Operations
Declaration:
int *ptr; // Declares a pointer to an integer
Initialization:
int x = 10;
int *ptr = &x; // `ptr` now holds the address of `x`
Dereferencing:
Access the value stored at the address pointed
int value = *ptr; // Retrieves the value of `x` via `ptr`
Sample
#include <stdio.h>
int main() {
int a = 5; // Normal integer variable
int *p = &a; // Pointer `p` points to `a`
printf("Value of a: %d\n", a); // Output: 5
printf("Address of a: %p\n", (void*)&a); // Output: address of `a`
printf("Value of p: %p\n", (void*)p); // Output: address of `a`
printf("Value pointed to by p: %d\n", *p); // Output: 5
*p = 10; // Modifies `a` through the pointer
printf("New value of a: %d\n", a); // Output: 10
return 0;
}
Pointer to a pointer
int x = 10;
int *ptr = &x;
int **pptr = &ptr; // Pointer to pointer
Pointer to a struct
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// Define a structure
struct Person {
char name[50];
int age;
};
int main() {
// Declare a pointer to a structure
struct Person *ptr;
// Allocate memory for the structure
ptr = (struct Person *)malloc(sizeof(struct Person));
if (ptr == NULL) {
printf("Memory allocation failed\n");
return 1;
}
// Use the arrow operator to access and set structure members
strcpy(ptr->name, "Alice");
ptr->age = 30;
// Print structure members
printf("Name: %s\n", ptr->name);
printf("Age: %d\n", ptr->age);
// Free allocated memory
free(ptr);
return 0;
}
Keywords
extern
It is used to declare a global variable or function that is defined in another file or later in the same file.
#include <stdio.h>
int main() {
extern int a; // Accesses a variable from outside
printf("%d\n", a);
return 0;
}
int a = 20;
static
Global Static Variables:
A global static variable is declared outside of any function with the static keyword.
The scope is limited to the file in which it is declared. This means it is not accessible from other files. If not explicitly initialized, a global static variable is automatically initialized to zero.
#include <stdio.h>
static int global_var = 10; // Global static variable
void display(void) {
printf("Global variable: %d\n", global_var); // Accesses global static variable
}
int main(void) {
display(); // Prints 10
global_var = 20;
display(); // Prints 20
return 0;
}
Local Static Variables
A local static variable is declared inside a function with the static keyword.
The scope is limited to the function in which it is declared. It cannot be accessed from outside the function.If not explicitly initialized, a local static variable is automatically initialized to zero.
#include <stdio.h>
void counter(void) {
static int count = 0; // Local static variable
count++;
printf("Count: %d\n", count); // Prints the current value of count
}
int main(void) {
counter(); // Prints 1
counter(); // Prints 2
counter(); // Prints 3
return 0;
}
Note: In C, when you have a global and a local variable with the same name, the local variable shadows (or hides) the global variable within its scope.
struct
struct book
{
char name[10];
float price;
int pages;
};
typedef
It is used to create alias name for an existing type
typedef unsigned int uint;
int main() {
uint x = 10; // Equivalent to unsigned int x = 10;
printf("x = %u\n", x);
return 0;
}
typedef struct Ntype {
int i;
char c;
long x;
} NewType;
Linkage
It refers to the visibility of symbols (variables and functions) across source files
External Linkage: The symbol is visible across multiple translation units (global)
Internal Linkage: The symbol is visible only within the translation unit where it is defined
None (No Linkage): The symbol is not visible outside the block in which it is defined (local variables)
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