Variables

Theory

C is a statically typed language — every variable must be declared with its type before use. The type determines how much memory is allocated and what operations are allowed.

Basic data types:

• int — integer (typically 4 bytes, range -2^31 to 2^31-1)
• float — single-precision floating-point (4 bytes)
• double — double-precision floating-point (8 bytes)
• char — single character (1 byte, stores ASCII value)

Modifiers alter the range or size: short, long, unsigned, signed.

unsigned int positive = 100;
long big_number = 1000000;
short small = 10;

Variable declaration and initialization:

int age;           // declaration
age = 25;          // initialization
int count = 0;     // declaration + initialization

Constants are values that cannot change:

• const keyword: const int DAYS = 7;
• #define preprocessor: #define PI 3.14159

The sizeof operator returns the size of a type or variable in bytes.

Format specifiers are used with printf() and scanf():

• %d — int
• %f — float
• %lf — double
• %c — char
• %s — string (char array)
• %u — unsigned int
• %ld — long int

printf() prints formatted output. scanf() reads formatted input from the keyboard. scanf requires the addresses of variables (using &).

Type conversion happens when different types are mixed:

• Implicit conversion (automatic): int + float → float
• Explicit conversion (casting): (float)int_var

Type casting syntax: (type)value

int a = 5;
int b = 2;
float result = (float)a / b;  // 2.5, not 2

Practical Examples

Exercises

#include <stdio.h>\n\nint main() {\n  float length = 5.5;\n  float width = 3.2;\n  // Calculate area and perimeter\n  return 0;\n}

Rectangle: 5.50 x 3.20\nArea: 17.60\nPerimeter: 17.40

#include <stdio.h>\n\nint main() {\n  int a, b;\n  // Your code here\n  return 0;\n}

Enter first number: 15\nEnter second number: 4\nSum: 19\nDifference: 11\nProduct: 60\nQuotient: 3.75

Enter a character: #\nASCII value: 35\nPattern:\n  #\n ###\n#####

Mini Quiz

Mini Project