C Syntax Notes

Basic Structure of a C Program

#include <stdio.h>
int main() {
// Code goes here
return 0;
}

Comments

Single-line comment: // This is a comment
Multi-line comment: /* This is a comment */

Data Types

Basic Types: int, float, double, char
Modifiers: short, long, signed, unsigned
Void: void (for no return type or empty parameter lists)

Variable Declaration

int x;
float y;
char ch;
const int x = 1; //constant

Input

scanf("%d", &x);

Here, %d refers to the datatype of the input variable & x refers to the input variable.

%d: Integer

%l: Long

%ld: Long Integer

%lld: Long Long Integer

%f: float

%lf: Double

%c: Character

%s: string

Output

printf("Hello, World!\n");

Operators

Arithmetic: +, -, *, /, %
Relational: ==, !=, <, >, <=, >=
Logical: &&, ||, !
Assignment: =, +=, -=, *=, /=, %=
Increment/Decrement: ++, —
Bitwise: &, |, ^, ~, <<, >>

Control Structures

Conditional Statements:

if (condition) {
// code
} else if(condition) {
// code
} else {
// code
}

Switch Case:

switch (expression) {
case value1:
// code
break;
case value2:
// code
break;
default:
// code
}

Loops

For loop

for (initialization; condition; update) {
// code
}

While loop

while (condition) {
// code
}

Do-While loop

do {
// code
} while (condition);

Functions

Function Declaration:

return_type function_name(parameters);

Function Definition:

return_type function_name(parameters) {
// code
}

Function Call:

function_name(arguments);

Pointers

Declaration: int *ptr;
Initialization: ptr = &x;
Dereferencing: *ptr

Function Pointers

void (*funcPtr)(int);
funcPtr = &functionName;

Arrays

Declaration:

int arr[10]; // Declaring an array of size 10

Accessing Elements:

arr[0] = 5;

Strings

Declaration:

char str[20]; // Declares a string with space for 20 characters

Initialization:

char str[] = "Hello";

Structures

Declaration:

struct StructName {
data_type member1;
data_type member2;
};

Accessing Members:

struct StructName s;
s.member1 = value;

Unions

Declaration:

union UnionName {
data_type member1;
data_type member2;
};

Accessing Members:

union UnionName u;
u.member1 = value;

Typedef

Creating an Alias for a Data Type:

typedef unsigned long int ULI;
ULI number;

Enums

Declaration:

enum Day {Sunday, Monday, Tuesday};
enum Day today;

File Handling

Opening a File:

FILE *filePointer = fopen("filename.txt", "r");

Closing a File:

fclose(filePointer);

Preprocessor Directives

Includes: #include <stdio.h>
Define Constants: #define PI 3.14

Dynamic Memory Allocation

int *ptr = (int*) malloc(size * sizeof(int));
free(ptr);

sizeof Operator

int size = sizeof(variable);