Basic Python Programs

print, input, if, a bit of math. Week-one stuff. If this feels slow, skip ahead.

25 programs · open one, then the next

The matching chapter is Day 1: Introduction to Python in the Python course. For a short check, try the Python quiz (300 questions). Every topic is listed on Python exercises.

Start with Print "Hello, World!"

01Print "Hello, World!"BeginnerOne print. If this runs, Python is actually installed.Open example →py# if this prints, Python is installed print("Hello, World!")
02Add Two NumbersBeginnerinput() gives strings. Forget float() and you glue 10 and 20 into 1020.Open example →py# Program to add two numbers provided by the user # taking input from the user num1 = float(input("Enter first number: "))
03Swap Two VariablesBeginnerThe textbook temp-variable swap, then the one-liner you will actually use.Open example →py# Swapping using a temporary variable a = 5 b = 10
04Find ASCII Value of a CharacterBeginnerord('A') is 65. Type two characters and this program refuses.Open example →py# Program to find the ASCII value of a character ch = input("Enter a character: ")
05Check Even or OddBeginnernum % 2. Remainder 0 means even. That is the whole trick.Open example →py# Program to check if a number is even or odd num = int(input("Enter an integer: "))
06Find Largest of Two NumbersBeginnerThree cases: a bigger, b bigger, or they match. The equal case is the one people skip.Open example →py# Program to find the largest of two numbers a = float(input("Enter first number: ")) b = float(input("Enter second number: "))
07Find Largest of Three NumbersBeginnera vs b vs c. Use >= so ties don't fall through into the wrong variable.Open example →py# Program to find the largest of three numbers a = float(input("Enter first number: ")) b = float(input("Enter second number: "))
08Check Positive, Negative, or ZeroBeginnerZero is not positive. Put it in its own branch or you will lie to the user.Open example →py# Program to check if a number is positive, negative, or zero num = float(input("Enter a number: "))
09Convert Kilometers to MilesBeginnerMultiply by 0.621371. Put the magic number in a named variable so you can find it later.Open example →py# Program to convert kilometers to miles kilometers = float(input("Enter distance in kilometers: "))
10Convert Celsius to FahrenheitBeginnerF = C * 9/5 + 32. The parentheses are not optional in your head even if Python's precedence saves you.Open example →py# Program to convert Celsius to Fahrenheit celsius = float(input("Enter temperature in Celsius: "))
11Calculate Area of a TriangleBeginner0.5 * base * height. Height means perpendicular height, not a slanty side.Open example →py# Program to calculate the area of a triangle base = float(input("Enter the base of the triangle: ")) height = float(input("Enter the height of the triangle: "))
12Calculate Simple InterestBeginnerSI = P*R*T / 100. Rate is percent, so 5 means 5%, not 0.05.Open example →py# Program to calculate simple interest principal = float(input("Enter principal amount: ")) rate = float(input("Enter annual interest rate (in %): "))
13Calculate Compound InterestBeginnerA = P(1 + R/100n)^(nT). Then interest is A minus P. The ** is the whole point.Open example →py# Program to calculate compound interest principal = float(input("Enter principal amount: ")) rate = float(input("Enter annual interest rate (in %): "))
14Calculate Square RootBeginnermath.sqrt. Negative input: don't call it. Python will throw, not politely refuse.Open example →py# Program to calculate the square root of a number import math
15Convert Seconds to Hours, Minutes, and SecondsBeginner// 3600 for hours, % for leftovers. Same trick as making change.Open example →py# Program to convert seconds to hours, minutes, and seconds total_seconds = int(input("Enter total seconds: "))
16Calculate Body Mass Index (BMI)Beginnerweight / height². Height in metres. 175 cm is 1.75, not 175 — that BMI looks fatal.Open example →py# Program to calculate Body Mass Index (BMI) weight = float(input("Enter your weight in kg: ")) height = float(input("Enter your height in meters: "))
17Check Leap YearBeginnerDivisible by 4, except centuries, except 400. 1900 is not a leap year. 2000 is.Open example →py# Program to check if a year is a leap year year = int(input("Enter a year: "))
18Find Absolute ValueBeginnerIf it's negative, flip the sign. abs() exists; this is the if version.Open example →py# Program to find the absolute value of a number num = float(input("Enter a number: "))
19Calculate Age from Birth YearBeginnerthis year minus birth year. Wrong if your birthday hasn't happened yet. Close enough for a first program.Open example →py# Program to calculate age from birth year from datetime import date
20Sum of First N Natural NumbersBeginnerN(N+1)/2. A loop also works. The formula is O(1) and easier to get wrong with / vs //.Open example →py# Program to find the sum of first N natural numbers n = int(input("Enter a positive integer N: "))
21Calculate Power Without Using pow()BeginnerMultiply in a loop. Negative exponents: do the positive power, then 1/result.Open example →py# Program to calculate a^b without using pow() or ** for the core logic base = float(input("Enter the base (a): ")) exponent = int(input("Enter the exponent (b, integer): "))
22Print Multiplication TableBeginnerfor i in range(1, 11): print n * i. The `or 10` is the sneaky bit.Open example →py# Program to print multiplication table of a number num = int(input("Enter a number: ")) limit = int(input("Enter limit (default 10): ") or 10)
23Convert Decimal to BinaryBeginnerKeep dividing by 2, save the remainders, reverse them. bin(10) is 0b1010 if you are in a hurry.Open example →py# Program to convert decimal to binary without using bin() num = int(input("Enter a non-negative integer: "))
24Convert Binary to DecimalBeginnerLeft to right: double, add the bit. 1010 → 10. Reject anything that isn't 0 or 1.Open example →py# Program to convert binary to decimal without using int(x, 2) binary_str = input("Enter a binary number: ")
25Calculate Electricity BillBeginnerSlabs: first 100 at 5, next 100 at 7, rest at 10. 250 units should be 1850, not 2500.Open example →py# Program to calculate electricity bill using slab rates units = float(input("Enter electricity units consumed: "))