35 Important Python Programs

# 1. Simple interest and compound interest
p, r, t = 10000, 8, 3
si = p * r * t / 100
ci = p * (1 + r / 100) ** t - p
print('SI =', si, '| CI =', round(ci, 2))

# 2. Largest of three numbers
a, b, c = 42, 87, 63
print('Largest =', max(a, b, c))
if a >= b and a >= c:
    big = a
elif b >= c:
    big = b
else:
    big = c
print('Using if-elif =', big)

# 3. Roots of a quadratic equation ax^2 + bx + c = 0
a, b, c = 1, -7, 10
d = b * b - 4 * a * c
if d > 0:
    r1 = (-b + d ** 0.5) / (2 * a)
    r2 = (-b - d ** 0.5) / (2 * a)
    print('Real and different roots:', r1, r2)
elif d == 0:
    print('Equal roots:', -b / (2 * a))
else:
    print('Imaginary roots')

# 4. Leap year check for several years
for year in (1900, 2000, 2024, 2026):
    leap = (year % 4 == 0 and year % 100 != 0) or year % 400 == 0
    print(year, 'Leap' if leap else 'Not leap')

# 5. Grade from percentage
for pct in (95, 81, 67, 45, 28):
    if pct >= 90:   g = 'A'
    elif pct >= 75: g = 'B'
    elif pct >= 60: g = 'C'
    elif pct >= 33: g = 'D'
    else:           g = 'E'
    print(pct, '->', g)

# 6. Factorial using a loop
n = 7
f = 1
for i in range(1, n + 1):
    f *= i
print(n, '! =', f)

# 7. Fibonacci series up to 100
a, b = 0, 1
while a <= 100:
    print(a, end=' ')
    a, b = b, a + b
print()

# 8. Prime or composite
for n in (2, 15, 29, 49, 97):
    is_prime = n > 1
    for d in range(2, int(n ** 0.5) + 1):
        if n % d == 0:
            is_prime = False
            break
    print(n, 'Prime' if is_prime else 'Composite')

# 9. Armstrong numbers between 100 and 999
for n in range(100, 1000):
    s = sum(int(d) ** 3 for d in str(n))
    if s == n:
        print(n, end=' ')
print()

# 10. Perfect numbers below 10000
for n in range(2, 10000):
    if sum(d for d in range(1, n) if n % d == 0) == n:
        print(n, end=' ')
print()

# 11. Reverse, digit sum and palindrome
n = 48584
rev, s, t = 0, 0, n
while t > 0:
    d = t % 10
    rev = rev * 10 + d
    s += d
    t //= 10
print('Reverse:', rev, '| Digit sum:', s, '| Palindrome:', rev == n)

# 12. HCF (GCD) and LCM using Euclid's method
a, b = 84, 120
x, y = a, b
while y != 0:
    x, y = y, x % y
hcf = x
print('HCF =', hcf, '| LCM =', a * b // hcf)

# 13. Sum of series 1 + x + x^2/2! + x^3/3! ... (n terms)
x, n = 2, 8
term, total = 1, 1
for i in range(1, n):
    term = term * x / i
    total += term
print('Sum =', round(total, 4))

# 14. Sum of series 1 - 2 + 3 - 4 + ... n
n = 10
s = 0
for i in range(1, n + 1):
    s += i if i % 2 else -i
print('Sum =', s)

# 15. Decimal to binary without bin()
n = 45
b = ''
while n > 0:
    b = str(n % 2) + b
    n //= 2
print('Binary =', b)

# 16. Number pyramid
n = 5
for i in range(1, n + 1):
    print(' ' * (n - i) + ' '.join(str(j) for j in range(1, i + 1)))

# 17. Floyd's triangle
num = 1
for i in range(1, 5):
    for j in range(i):
        print(num, end=' ')
        num += 1
    print()

# 18. Diamond of stars
n = 4
for i in list(range(1, n + 1)) + list(range(n - 1, 0, -1)):
    print(' ' * (n - i) + '*' * (2 * i - 1))

# 19. Alphabet pattern
for i in range(5):
    print(' '.join(chr(65 + j) for j in range(i + 1)))

# 20. Count vowels, consonants, uppercase, lowercase
s = 'Python Is FUN to Learn'
v = sum(1 for ch in s if ch.lower() in 'aeiou')
c = sum(1 for ch in s if ch.isalpha() and ch.lower() not in 'aeiou')
print('Vowels:', v, 'Consonants:', c)
print('Upper:', sum(ch.isupper() for ch in s), 'Lower:', sum(ch.islower() for ch in s))

# 21. Palindrome string (ignore case and spaces)
s = 'Never odd or even'
clean = s.replace(' ', '').lower()
print(clean == clean[::-1])

# 22. Longest word and word count
s = 'Practice makes a programmer perfect'
words = s.split()
print('Words:', len(words), '| Longest:', max(words, key=len))

# 23. Replace every vowel with '*' and toggle case
s = 'Computer Science'
print(''.join('*' if ch.lower() in 'aeiou' else ch for ch in s))
print(s.swapcase())

# 24. Character frequency in a string
s = 'banana'
freq = {}
for ch in s:
    freq[ch] = freq.get(ch, 0) + 1
print(freq)

# 25. Caesar cipher (shift by 3)
s = 'HELLO WORLD'
enc = ''
for ch in s:
    if ch.isalpha():
        enc += chr((ord(ch) - 65 + 3) % 26 + 65)
    else:
        enc += ch
print(enc)

# 26. Max, min, mean of a list
L = [34, 78, 12, 56, 90, 45]
print('Max:', max(L), 'Min:', min(L), 'Mean:', round(sum(L) / len(L), 2))

# 27. Linear search returning index
L = [12, 45, 7, 33, 81]
key = 33
pos = -1
for i in range(len(L)):
    if L[i] == key:
        pos = i
        break
print(key, 'found at index', pos)

# 28. Swap elements at even and odd positions
L = [10, 20, 30, 40, 50, 60]
for i in range(0, len(L) - 1, 2):
    L[i], L[i + 1] = L[i + 1], L[i]
print(L)

# 29. Remove duplicates keeping order
L = [3, 5, 3, 8, 5, 9, 1, 8]
unique = []
for x in L:
    if x not in unique:
        unique.append(x)
print(unique)

# 30. Separate even and odd, and double each odd
L = [5, 12, 7, 20, 3, 8]
even = [x for x in L if x % 2 == 0]
odd = [x for x in L if x % 2]
print('Even:', even, 'Odd:', odd)
print('Odd doubled in list:', [x * 2 if x % 2 else x for x in L])

# 31. Count elements greater than average in a tuple
t = (23, 67, 45, 89, 12, 56)
avg = sum(t) / len(t)
print('Average:', avg, '| Above average:', sum(1 for x in t if x > avg))

# 32. Sum of each row and column of a matrix
M = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print('Row sums:', [sum(r) for r in M])
print('Column sums:', [sum(M[i][j] for i in range(3)) for j in range(3)])
print('Diagonal sum:', sum(M[i][i] for i in range(3)))

# 33. Students with marks above 75 from a dictionary
marks = {'Asha': 82, 'Ravi': 67, 'Neha': 91, 'Ishan': 74, 'Tara': 88}
for name, m in marks.items():
    if m > 75:
        print(name, m)

# 34. Count words in a sentence using a dictionary
s = 'to be or not to be'
count = {}
for w in s.split():
    count[w] = count.get(w, 0) + 1
print(count)

# 35. Employee salary dictionary: raise 10% and find highest
emp = {'E1': 32000, 'E2': 45000, 'E3': 28000}
for k in emp:
    emp[k] = round(emp[k] * 1.10)
print(emp)
top = max(emp, key=emp.get)
print('Highest paid:', top, emp[top])