Convert String to Integer and Vice Versa

1. The Challenge: Type Casting

Write two functions: string_to_int(txt) that converts a numerical string into an integer, and int_to_string(num) that converts an integer into a string.

2. Why It Matters

User inputs (from forms or command line arguments) enter Python as strings. Converting them to numbers is required before doing math operations.

3. The Python Solution

Use built-in int() and str() type casting functions:

def string_to_int(txt):
    return int(txt)

def int_to_string(num):
    return str(num)

# Testing string to int
print(string_to_int("6"), type(string_to_int("6"))) # Output: 6 <class 'int'>
print(string_to_int("1000"))                        # Output: 1000

# Testing int to string
print(int_to_string(45), type(int_to_string(45)))   # Output: '45' <class 'str'>

4. How Type Casting Operates

Python is strongly typed, meaning it will NOT implicitly convert "5" + 5 (this raises a TypeError). Explicit type casting via int() and str() is required.

5. Common Mistakes

• ValueError on Invalid String: Passing non-numeric text to int("hello") raises a ValueError: invalid literal for int() with base 10. Use try/except blocks when parsing unpredictable user input.

6. Next Steps

Use int() and str() for explicit type casting. Next, let's count words in a sentence!