Introduction to C Programming

int age;  // int is a data type for integer and age is the name of variable

Global Variable

Variables which are declared outside the main function block, and they can be used in the main program block and sub program block like functions.

Local Variable

Variables which are declared inside the main function block, and they are used only in the block in which they are declared. Sub programs or functions can also have local variables.

Initialization

When we declare a variable and give it a value at the same time, it's called initialization.

Example:

int age = 32;  // Declaration and initialization

Assignment

When we give a new value to an already declared variable, it's called assignment.

Example:

age = 25;  // Assigning a new value

Assignment is not limited to changing values. If a variable was declared but not initialized, we can assign a value to it later.

int age;     // Declaration without initialization
age = 30;    // Assignment after declaration

Numeric Constants

1. Integer Constant: An integer constant is a signed or unsigned whole number.

   Example: -24, 52, 102

2. Real or Floating Point Constant: Any signed or unsigned number with fractional part.

   Example: 3.14, 0.234, 0.42e-32

String or Character Constants

1. Single character string constant: Any letter or character enclosed in single quotes.

   Example: 'h', 'a', '+'

2. String of characters constant: Any string of characters consisting of letters, digits, and symbols enclosed in double quotes.

   Example: "letters", "number02", "person+name+$"

Arithmetic Operators

• + : addition, 1 + 1 = 2
• - : subtraction, 2 - 1 = 1
• * : multiplication, 2 * 3 = 6
• / : division, 8 / 2 = 4

Relational Operators

• < : less than : 5 < 2 : FALSE
• > : greater than : 5 > 2 : TRUE
• <= : less than or equal to : 5 <= 2 : FALSE
• >= : greater than or equal to : 5 >= 2 : TRUE
• == : equal to : 5 == 2 : FALSE or 5 == 5 : TRUE
• != : not equal to : 5 != 2 : TRUE

Logical Operators

&& : AND : Returns TRUE if all the given condition or statement are true, if any statement is false, it will always return FALSE

Example: (5<2) && (5>2) : FALSE

|| : OR : Return TRUE if any of the given condition or statement are true, if none of the condition is TRUE, it will always return FALSE

Example: (5<2) || (5>3) : TRUE

! : NOT : Return TRUE if the condition is FALSE, if the condition is TRUE, it will always return FALSE

Example: !(5<2) : TRUE

Truth Tables

AND (&&) Operator

OPERAND 1	OPERAND 2	RESULT
true	true	true
true	false	false
false	true	false
false	false	false

OR (||) Operator

OPERAND 1	OPERAND 2	RESULT
true	true	true
true	false	true
false	true	true
false	false	false

NOT (!) Operator

OPERAND	RESULT
true	false
false	true

Increment and Decrement

Increment

The increment operator in C is represented by the ++ symbol.

1. Pre-increment: ++variable

   The value of the variable is incremented by 1 before it is used in the expression.

   Example: x = ++y; (first increments y by 1, then assigns the new value of y to x)

2. Post-increment: variable++

   The value of the variable is used in the expression first, and then it is incremented by 1.

   Example: x = y++; (first assigns the current value of y to x, then increments y by 1)

Decrement

The decrement operator in C is represented by the -- symbol.

1. Pre-decrement: --variable

   The value of the variable is decremented by 1 before it is used in the expression.

   Example: x = --y; (first decrements y by 1, then assigns the new value of y to x)

2. Post-decrement: variable--

   The value of the variable is used in the expression first, and then it is decremented by 1.

   Example: x = y--; (first assigns the current value of y to x, then decrements y by 1)

Example

int x = 5;
int y = 10;

// Pre-increment
x = ++y;  // x = 11, y = 11

// Post-increment
x = y++;  // x = 11, y = 12

// Pre-decrement
x = --y;  // x = 11, y = 11

// Post-decrement
x = y--;  // x = 12, y = 11

Assignment Operators

In C programming, assignment operators are used to assign values to variables.

Simple Assignment (=)

Assigns the value on the right to the variable on the left.

int x = 10;  // x is now 10

Addition Assignment (+=)

Adds the right operand to the left operand and assigns the result to the left operand.

int x = 10;
x += 5;  // x is now 15 (10 + 5)

Subtraction Assignment (-=)

int x = 10;
x -= 3;  // x is now 7 (10 - 3)

Multiplication Assignment (*=)

int x = 10;
x *= 2;  // x is now 20 (10 * 2)

Division Assignment (/=)

int x = 10;
x /= 2;  // x is now 5 (10 / 2)

Modulus Assignment (%=)

int x = 10;
x %= 3;  // x is now 1 (10 % 3)

Conditional (Ternary) Operator

Conditional Operator or Ternary operator is used to check a condition and select a value depending on the condition. It's a shorter version of if-else statement.

Syntax: (condition) ? value1 : value2;

If the condition is TRUE it will execute the value1 and if the condition is FALSE it will execute the value2.

Comparison: Ternary vs If-Else

Ternary

int a = 10;
int b = 15;
int big;

big = (a > b) ? a : b;

If-Else

int a = 10;
int b = 15;
int big;

if (a > b) {
  big = a;
} else {
  big = b;
}

Bitwise Operators

Recommended not to focus much on these as they are for advanced programmers who manages data at bit level.
Some research on Binary numbers and Base 2 number system will help understand these better!

Bitwise Operators in C

Operator	Name	Description
&	AND	1 if both bits are 1
|	OR	1 if at least one bit is 1
^	XOR	1 if only one of the bits is 1
~	NOT	Flips all bits (0 becomes 1, and 1 becomes 0)
<<	Left Shift	Shifts bits left, fills 0s on the right
>>	Right Shift	Shifts bits right, removes bits from the end

Example

#include <stdio.h>

int main() {
    int a = 5;   // Binary: 00000101
    int b = 3;   // Binary: 00000011

    printf("a & b = %d\n", a & b);  // 00000001 → 1
    printf("a | b = %d\n", a | b);  // 00000111 → 7
    printf("a ^ b = %d\n", a ^ b);  // 00000110 → 6
    printf("~a = %d\n", ~a);        // In 8-bit: 11111010 → -6 (2's complement)
    printf("a << 1 = %d\n", a << 1); // 00001010 → 10
    printf("a >> 1 = %d\n", a >> 1); // 00000010 → 2

    return 0;
}

Variable Declaration

// Declaring a variable 
// We use a type specifier to declare a variable [int, char, float, double] choose the required type

int age = 25; // int for age as it is integer
char name[20] = "tomba"; // We are using array - it's just a collection of many char
float pi = 3.14; // We are using float for decimal numbers

Simple Hello World Structure

#include <stdio.h>

int main() {
  printf("Hello world\n");
  return 0;
}

Output

Hello world

Here the code starts with the include <stdio.h> which includes the standard input/output header file that provides the printf function. We use int main as the return type and the printf function to print the words inside the double quotes. '\n' means move to new line and we give a return value 0 which tells the OS that the program ran successfully.