Programming Essentials in C - Lecture 3

C Constants

• Constants are values that cannot be changed once assigned.
• Declared using the const keyword.
• Typically named in uppercase for readability.

Declaring Constants

Example:

const float PI = 3.14; // Constant float
const int BIRTH_YEAR = 2005; // Constant integer

printf("%.2f\n", PI); // Output: 3.14
printf("%d\n", BIRTH_YEAR); // Output: 2005
PI = 3.14159; // Error: cannot modify constant

C Type Conversion

Type conversion in C involves converting a value from one data type to another.
There are two types:

• Implicit Conversion (automatic)
• Explicit Conversion (manual)

Implicit Conversion

Implicit conversion is done automatically by the compiler when assigning a value of one type to another.

Example:

// Integer 9 is implicitly converted to float
float num = 9;
printf("%f", num); // Output: 9.000000

Another example where float is automatically converted to int:

// Integer division, drops decimal (2.5 -> 2)
int result = 5 / 2;
printf("Integer division: %d\n", result); // Output: 2

This may lead to data loss if not handled carefully.

Explicit Conversion

Explicit conversion (casting) is performed manually by specifying the target type in parentheses before the value or variable.

Example:

// Forces floating-point division
float result = (float) 5 / 2;
result = 5.0 / 2; // this also works

printf("%f", result); // output: 2.500000

Real-Life Example

Calculate a user's score percentage in a game:

const int MAX_SCORE = 500; // Maximum possible score
int userScore = 423;       // User's score

float percentage = (float) userScore / MAX_SCORE * 100.0; // Explicit cast for precision
printf("User's percentage: %.2f%%", percentage); // Output: 84.60%

C Operators

Operators are symbols that instruct the compiler to perform specific mathematical or logical operations.

Arithmetic Operators

Arithmetic operators perform basic math operations.

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
/	Division
%	Modulus
++	Increment
--	Decrement

Example:

int a = 10, b = 3;
printf("a: %d, b: %d\n", a, b);
printf("Addition: %d\n", a + b);       // 13
printf("Subtraction: %d\n", a - b);    // 7
printf("Multiplication: %d\n", a * b); // 30
printf("Division: %d\n", a / b);       // 3
printf("Modulus: %d\n", a % b);        // 1

Arithmetic Operations with char

char values (stored as ASCII integers) can be used in arithmetic operations.

Example:

char first = 'Z', second = 'M';
// 90 - 77 = 13 (ASCII values)
int diff = first - second;
printf("Difference between '%c' and '%c': %d\n", first, second, diff);

Relational Operators

Relational operators compare two values and return a boolean result (1 for true, 0 for false).

Operator	Description	Example
==	Equal to	5 == 5
!=	Not equal to	5 != 3
>	Greater than	5 > 3
<	Less than	5 < 6
>=	Greater than or equal to	5 >= 5
<=	Less than or equal to	5 <= 6

Example:

int x = 15, y = 10;
printf("x == y: %d\n", x == y); // 0
printf("x != y: %d\n", x != y); // 1
printf("x > y: %d\n", x > y);   // 1
printf("x < y: %d\n", x < y);   // 0

Logical Operators

Logical operators combine conditions to produce a true (1) or false (0) result.

Operator	Description	Example
&&	Logical AND	A && B
||	Logical OR	A || B
!	Logical NOT	!A

Example:

int english = 50, maths = 60;
if (english >= 50 && maths >= 50) {
  printf("Result: Pass\n"); // Output: Pass
} else {
  printf("Result: Fail\n");
}

Bitwise Operators

Bitwise operators manipulate individual bits of numbers.

Operator	Description	Example
&	Bitwise AND	A & B
|	Bitwise OR	A | B
^	Bitwise XOR	A ^ B
~	Bitwise NOT (complement)	~A
<<	Left shift	A << 2
>>	Right shift	A >> 2

Example:

unsigned int a = 60; // 0011 1100
unsigned int b = 13; // 0000 1101
printf("a & b: %d\n", a & b);   // 12 (0000 1100)
printf("a | b: %d\n", a | b);   // 61 (0011 1101)
printf("a ^ b: %d\n", a ^ b);   // 49 (0011 0001)
printf("~a: %d\n", ~a);         // -61 (1100 0011)
printf("a << 2: %d\n", a << 2); // 240 (1111 0000)
printf("a >> 2: %d\n", a >> 2); // 15 (0000 1111)

Assignment Operators

Assignment operators assign values to variables, often combined with arithmetic or bitwise operations.

Operator	Example	Equivalent To
=	x = 5	x = 5
+=	x += 3	x = x + 3
-=	x -= 3	x = x - 3
*=	x *= 3	x = x * 3
/=	x /= 3	x = x / 3
%=	x %= 3	x = x % 3
&=	x &= 3	x = x & 3
|=	x | = 3	x = x | 3
^=	x ^= 3	x = x ^ 3
<<=	x <<= 3	x = x << 3
>>=	x >>= 3	x = x >> 3

Example:

int a = 21, b;
b = a;     printf("b = a: %d\n", b);    // 21
b += a;    printf("b += a: %d\n", b);   // 42
b -= a;    printf("b -= a: %d\n", b);   // 21
b *= a;    printf("b *= a: %d\n", b);   // 441
b /= a;    printf("b /= a: %d\n", b);   // 21
b = 200;
b %= a;    printf("b %%= a: %d\n", b);  // 11

Increment and Decrement Operators

These operators increment or decrement the value of a variable by 1.

Types

1. Pre-increment/decrement: Changes value before use (++a, --a)
2. Post-increment/decrement: Changes value after use (a++, a--)

Example:

int a = 5, pre, post;

pre = ++a;
// a = 6, pre = 6
printf("Pre-increment: a = %d, pre = %d\n", a, pre);

a = 5;
post = a++;
// a = 6, post = 5
printf("Post-increment: a = %d, post = %d\n", a, post);

a = 5;
pre = --a;
// a = 4, pre = 4
printf("Pre-decrement: a = %d, pre = %d\n", a, pre);

a = 5;
post = a--;
// a = 4, post = 5
printf("Post-decrement: a = %d, post = %d\n", a, post);