👨💻 Programming Basics
Algorithms, flowcharts, Python emulator with 8 examples.
👨💻 Writing Instructions for Computers
Programming is the process of writing instructions (code) that a computer can execute. A program is a set of instructions. A programming language is the syntax used to write those instructions.
Levels of language:
• Machine Language — binary (0s and 1s). Directly understood by CPU. Fastest but unreadable.
• Assembly Language — mnemonics (MOV, ADD). Converted to machine code by assembler.
• High-level Language — human-readable (Python, C, Java). Converted by compiler or interpreter.
Compiler — translates entire program at once (C, C++). Interpreter — translates line-by-line (Python, JavaScript).
Algorithm — step-by-step solution to a problem. Properties: input, output, definiteness, finiteness, effectiveness.
Flowchart — visual representation of algorithm. Symbols: Oval (start/end), Rectangle (process), Diamond (decision), Parallelogram (I/O), Arrow (flow).
Variables: x = 5 | name = "Ravi" | pi = 3.14
Data types: int (5), float (3.14), str ("hello"), bool (True/False), list ([1,2,3]), dict ({key:val})
Input/Output: print("Hello") | name = input("Enter name: ")
If-else: if x > 0: ... elif x == 0: ... else: ...
Loops: for i in range(5): ... | while condition: ...
Functions: def greet(name): return "Hello " + name
Lists: nums = [1,2,3] | nums.append(4) | len(nums)
Variable — named memory location. Constant — value doesn't change.
Operator types: Arithmetic (+,-,*,/,//,%,**), Relational (==,!=,>,<), Logical (and, or, not), Assignment (=,+=,-=)
Array — collection of same-type elements. Index starts from 0.
Function/Procedure — reusable block of code. Function returns value, procedure does not.
Recursion — function calling itself. Base case prevents infinite recursion.
OOP concepts: Class, Object, Inheritance, Encapsulation, Polymorphism, Abstraction.
Flowchart Symbols & Algorithm Design
AnimationThis flowchart checks if N is even (N%2==0). Now try coding it below in the Python emulator!
Python Emulator — Run Code in Browser
InteractiveWrite Python code below and click ▶ Run to execute. Supports print(), input(), loops, functions, lists and more.
def is_prime(n):
if n < 2:
return False
for i in range(2, int(n**0.5) + 1):
if n % i == 0:
return False
return True
# Test the function
for num in range(1, 20):
if is_prime(num):
print(num, "is prime")
# Output: 2, 3, 5, 7, 11, 13, 17, 19
Key insight: We only need to check divisors up to √n. If n has a factor greater than √n, its corresponding factor must be less than √n — so we would have already found it. This makes the algorithm O(√n) instead of O(n).
• Translates entire source code into machine code ALL AT ONCE before execution
• Creates an executable file (.exe, .out)
• Errors shown after complete compilation
• Faster execution (already translated)
• Languages: C, C++, Go, Rust, Fortran
• Example: gcc program.c -o program → ./program
Interpreter:
• Translates and executes source code LINE BY LINE
• No separate executable file created
• Errors shown as soon as problematic line is reached
• Slower execution (translates each time)
• Easier for debugging — immediate feedback
• Languages: Python, JavaScript (browser), Ruby, PHP
• Example: python3 program.py
Hybrid approach (Java):
• Java compiler converts to bytecode (.class file)
• JVM (Java Virtual Machine) interprets bytecode
• "Write once, run anywhere" — bytecode runs on any OS with JVM
Modern Python uses CPython which compiles to bytecode (.pyc) first, then interprets.
Modern JS engines (V8 in Chrome) JIT-compile JavaScript for speed.