K&R - Chapter 0 - Introduction using Python (Part 1)

Python and C Comparison

Similarities Between Python and C

Arithmetic Operators: +, -, *, /, %

Comparison Operators: <, >, <=, >=, !=

Variable Naming Rules:

• Case matters (e.g., myVar is different from myvar).
• Can use letters, numbers, and underscores in variable names, but they cannot start with a number.

Control Flow:
While Loops: Both languages have while loops and support the break and continue statements.

i = 0
while i < 5:
    if i == 3:
        break
    print(i)
    i += 1

int i = 0;
while (i < 5) {
    if (i == 3) {
        break;
    }
    printf("%d\n", i);
    i++;
}

Constants:
Both Python and C allow defining constants.
While Python has a convention for constants (uppercase variable names),
C uses #define or const to define constants.

MAX_VALUE = 100

#define MAX_VALUE 100

Data Types:
Integers and Floats: Both languages support integer and floating-point types.
In C, the int and float types exist, while in Python, all numbers are represented as int or float (and Python’s float is equivalent to C’s double).

Characters:
C has char for single characters, while Python uses strings,
but a single character in Python is a string of length 1.

Key Differences Between Python and C

Boolean Operators:
In Python, and, not, or are used for boolean operations.
In C, && (and), ! (not), || (or) are used.

a = True
b = False
if a and b:
print("Both are true")

int a = 1, b = 0;
if (a && b) {
	printf("Both are true\n");
	}

For Loops:
Python has a for..in loop for iterating over elements of a list or other iterable objects.

for i in range(5):
    print(i)

C does not have a for..in loop. Instead, you need to specify a loop variable, condition, and update manually:

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

Boolean Values:
Python has predefined constants True and False as boolean values.
In C, there are no predefined True or False values;
typically, 1 is used for true and 0 for false.

if True:
    print("True")

if (1) {
    printf("True\n");
}

None vs NULL:

• None in Python is a special object that represents the absence of a value. It is its own type.
• NULL in C is a null pointer constant, typically represented as 0 or ((void*)0).
  It represents a pointer that does not point to any memory address.

x = None
if x is None:
	print("x is None")

int* x = NULL;
if (x == NULL) {
    printf("x is NULL\n");
}

Strings and Character Arrays:

• Strings in Python are immutable and can be treated as objects with many built-in methods.
• C strings are arrays of characters, terminated by a null character ('\0'). String manipulation in C is less intuitive and requires careful handling of memory.

s = "Hello"
print(s.upper())

char s[] = "Hello";
printf("%s\n", strupr(s));  
// Requires external string manipulation functions like `strupr()`

Data Structures:
Python comes with built-in data structures like list and dict, which are high-level and flexible.
In C, you must manually define data structures using struct, and dynamic data structures often require the use of pointers for manipulation.

my_list = [1, 2, 3]
my_dict = {"key": "value"}

struct Point {
    int x;
    int y;
};

struct Point p = {1, 2};

Memory Management:
Python has automatic memory management with garbage collection, meaning memory is allocated and freed automatically.
C requires manual memory management using functions like malloc() for allocation and free() for deallocation.

a = [1, 2, 3]  # Memory management handled by Python

int* arr = (int*) malloc(3 * sizeof(int));  // Manual allocation
free(arr);  // Manual deallocation

No double in Python:
Python uses float for both single-precision and double-precision floating-point numbers, while C has both float (single precision) and double (double precision) types.

a = 3.14159  # Python float (equivalent to C's double)

double a = 3.14159;  // C double