C Programming Sticky Notes

Basic Structure

#include <stdio.h>

int main() {
  printf("Hello, World!");
  return 0;
}

Preprocessor

#include: Includes header files like <stdio.h>, <string.h>, <math.h>,<conio.h> etc.
#define: Defines constants.

Variables

Declaration:
int age;
Initialization:
char grade = 'A';

printf & scanf

printf (Output)
printf("Age: %d", age);

scanf (Input)
scanf("%d", &age);
Note: Always use the address-of operator (`&`) for variables.

Data Types & Ranges

Sizes: int(2/4), float(4), double(8), char(1) bytes.
char: -128 to 127
int (16-bit): -32k to 32k
int (32-bit): -2B to 2B
float: 3.4E-38 to 3.4E+38
double: 1.7E-308 to 1.7E+308

Operators

Arithmetic: + - * / %
Relational: == != > < >= <=
Logical: && || !
Bitwise: & | ^ ~ << >>

Type Conversion

Implicit:Low —> High, no loss of data.
int + float = float;
Explicit (Casting):High —> Low, loss of data.
int a = (int)10.5;

Control Structures

Conditional:
if, else if, else
switch-case-break
Unconditional:
break, continue, return, goto
Loops:
for, while, do-while

Functions

Declaration:
int add(int, int);
Call:
int sum = add(5, 3);
Supports call by value & call by reference.

Types of Functions

1. No args & no return
2. With args & no return
3. No args & with return
4. With args & with return

Pointers

Stores the memory address of another variable.

int x = 10;
int *ptr = &x;

*ptr gets the value at x.

Arrays

Collection of same-type elements.
1D: int a[5] = {10, 20};
2D:

int b[2][3] = {
  {1, 2, 3}, 
  {4, 5, 6}
};

Strings

Array of characters ending with `\0`.
char name[] = "Imad";
use string.h for string functions like strlen, strcpy, strcat.
Note: No '&' in 'scanf '.

String I/O Functions

gets: Reads a line (Unsafe!)
puts: Writes a string + `\n`
fgets: Safely reads a line from a stream.
fputs: Writes a string to a stream.

Structures

Collection of different data types. Each member has its own memory location.

struct Student {
    int id;
    char name[50];
};
struct Student s1;
s1.id = 101;

Unions

Collection of different data types in the same memory location. Only one member can hold a value at any given time.

union Data {
    int i;
    char str[20];
};

Typedef

Creates an alias for a data type.

typedef struct {
    int id;
    char name[20];
} Student;

Student s1;

Enum

Assigns names to integer constants.

enum Day {SUN, MON};
enum Day d = MON;

Note: Sturcture, Union and Enum are user-defined data types.

File Handling

FILE *fp;
fp = fopen("file.txt", "w");

fprintf(fp, "Text");
fscanf(fp, "%d", &var);

fclose(fp);

File Modes

"r": Read Only (must exist)
"w": Write Only (overwrites)
"a": Append Only (creates)
"r+": Read & Write
"w+": Write & Read (overwrites)
"a+": Append & Read

Recursion

A function that calls itself.

return_type func(params) {
  if (base_case)
    return value;
  else
    return func(new_params);
}