C Programming Cheat Sheet

Basic Structure of a C Program

Every C program follows a simple structure that includes header files, the main function, and program statements.

#include <stdio.h>

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

Key Components

Component	Description
#include	Includes header files
main()	Entry point of the program
printf()	Displays output
return 0	Ends the program

C Data Types Cheat Sheet

Data types specify the type of data that a variable can store.

Data Type	Example	Description
int	int a = 10;	Stores integer values
float	float x = 3.14;	Stores decimal numbers
double	double d = 12.567;	Higher precision decimal
char	char c = 'A';	Stores a single character

Data Type Size (Typical)

Type	Size
char	1 byte
int	4 bytes
float	4 bytes
double	8 bytes

Format Specifiers Cheat Sheet

Format specifiers are used with input and output functions such as printf() and scanf().

Specifier	Meaning
%d	Integer
%f	Float
%lf	Double
%c	Character
%s	String

Example:

printf("%d", number);

C Operators Cheat Sheet

Operators perform operations on variables and values.

Arithmetic Operators

Operator	Example
+	Addition
-	Subtraction
*	Multiplication
/	Division
%	Modulus

Example

int sum = a + b;

Relational Operators

Used for comparison.

Operator	Meaning
==	Equal
!=	Not equal
>	Greater than
<	Less than
>=	Greater or equal
<=	Less or equal

Logical Operators

Operator	Meaning
&&	Logical AND
||	Logical OR
!	Logical NOT

Conditional Statements Cheat Sheet

If Statement

if(a > b){
 printf("A is greater");
}

If Else Statement

if(a > b)
 printf("A is greater");
else
 printf("B is greater");

Switch Statement

switch(n){
 case 1:
  printf("One");
  break;

 default:
  printf("Invalid");
}

Loops Cheat Sheet

For Loop

for(int i=0;i<5;i++){
 printf("%d",i);
}

While Loop

while(i<5){
 printf("%d",i);
 i++;
}

Do While Loop

do{
 printf("%d",i);
 i++;
}while(i<5);

Arrays Cheat Sheet

int arr[5] = {1,2,3,4,5};
printf("%d", arr[0]);

Array Syntax

datatype array_name[size];

Example

int numbers[10];

Strings in C

In C, strings are stored as character arrays.

char name[20] = "IIES";
printf("%s", name);

Important String Functions

Function	Description
strlen()	Length of string
strcpy()	Copy string
strcat()	Concatenate strings
strcmp()	Compare strings

Functions Cheat Sheet

int add(int a,int b){
 return a + b;
}

Function Call

int result = add(5,3);

Pointers Cheat Sheet

int a = 10;
int *p = &a;

printf("%d", *p);

Symbol	Meaning
&	Address of variable
*	Pointer value

Pointers are very important in embedded systems and system programming.

Dynamic Memory Allocation

C allows dynamic memory allocation using functions from stdlib.h.

int *ptr;

ptr = (int*)malloc(5 * sizeof(int));

free(ptr);

Function	Purpose
malloc()	Allocate memory
calloc()	Allocate and initialize memory
realloc()	Resize memory
free()	Deallocate memory

Structures Cheat Sheet

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

Example

struct Student s1;
s1.id = 1;

Storage Classes Cheat Sheet

Storage Class	Description
auto	Default local variable
static	Retains value between function calls
extern	Global variable declaration
register	Stored in CPU register

Bitwise Operators Cheat Sheet

Operator	Meaning
&	AND
|	OR
^	XOR
~	NOT
<<	Left shift
>>	Right shift

Example

int result = a & b;

File Handling Cheat Sheet

FILE *fp;

fp = fopen("data.txt","w");

fprintf(fp,"Hello");

fclose(fp);

Mode	Description
r	Read
w	Write
a	Append

Important C Header Files

Header File	Purpose
stdio.h	Input Output
stdlib.h	Memory management
string.h	String operations
math.h	Mathematical functions
time.h	Time functions

Common Escape Characters

Escape characters are used inside strings.

Escape Character	Meaning
\n	New line
\t	Tab
\	Backslash
"	Double quote

Example

printf("Hello\nWorld");

C Keywords Cheat Sheet

C language contains reserved keywords that cannot be used as variable names.

Some common C keywords include:

int, char, float, double, if, else, switch, case, break, continue, return, struct, typedef, static, extern

C Programming Interview Topics

Students preparing for programming interviews should revise the following topics:

• pointers and pointer arithmetic
• stack vs heap memory
• dynamic memory allocation
• recursion
• arrays and strings
• structures and unions
• file handling

These topics are frequently asked in technical interviews and embedded systems programming roles.

Who Should Use This Cheat Sheet

This C programming quick reference guide is useful for:

• beginners learning C programming
• engineering students
• embedded systems learners
• programmers preparing for interviews
• developers needing quick syntax reference