19. Remove Trailing Zeros | Basic I/O

📝 Problem

Get a floating point value and print the floating point value without any trailing zeros.

Input Format:
Get a floating point value as input

Output Format:
Display the floating point value without trailing zeros

Constraints:
2.3E-308 to 1.7E+308

🎯 Why Mix C and C++? Smart Solutions with Limited Tools!

The Real-World Lesson

This problem teaches an important programming principle: when your current toolset is limited, sometimes borrowing from related technologies is the smartest solution!

💡 Why This Problem is Special

With basic C++ (cout and iomanip), removing trailing zeros is surprisingly difficult. But C's printf has a built-in format specifier (%g) that does this automatically! This is a perfect example of pragmatic programming.

1️⃣ Understanding the %g Format Specifier

The %g specifier is magical for this task:

✅ Automatically removes trailing zeros
✅ Removes trailing decimal point if no fractional part
✅ Uses shortest representation (decimal or scientific)
✅ Smart formatting based on the number's magnitude

2️⃣ How %g Works - Examples

Input	With %f	With %g
`23.0900`	`23.090000`	`23.09`
`12.5200`	`12.520000`	`12.52`
`100.0`	`100.000000`	`100`
`0.00056`	`0.000560`	`0.00056`

3️⃣ C vs C++ I/O - Quick Comparison

Feature	C Style	C++ Style
Input	`scanf("%lf", &num)`	`cin >> num`
Output	`printf("%g", num)`	`cout << num`
Header	`<cstdio>`	`<iostream>`
Type Safety	❌ No (manual format)	✅ Yes (automatic)
Trailing Zeros	✅ Easy with %g	❌ Complex

4️⃣ Understanding scanf and printf

scanf Syntax:

double num;
scanf("%lf", &num);  // %lf = long float (double)
                               // & = address-of operator

printf Format Specifiers:

// %f  - Fixed decimal (6 decimals default)
// %e  - Scientific notation
// %g  - Shortest representation (removes trailing zeros!)
// %lf - For double in scanf (not printf)

5️⃣ Why scanf Uses & (Address-Of)

scanf needs the memory address to store the value:

double num;
scanf("%lf", &num);  // & gives memory location
                    // scanf writes directly to that location

// Without & it would pass the value (wrong!)
// With & it passes the address (correct!)

6️⃣ Is Mixing C and C++ Bad Practice?

                            Short answer: No, but use wisely!
                            ✅ C++ is backward-compatible with C by design
✅ Sometimes C functions are simpler for specific tasks
✅ Many professional codebases mix both
⚠️ Don't mix scanf/printf with cin/cout in same program (buffering issues)
⚠️ Prefer C++ style when possible for type safety

                        

7️⃣ Alternative: Pure C++ Solution (Advanced)

For reference, here's the complex C++ way (you don't need this for basic problems!):

// Complex C++ approach (avoid for beginners)
double num;
cin >> num;
string str = to_string(num);
// Remove trailing zeros manually...
// Much more code needed!

✅ Key Takeaways

%g automatically removes trailing zeros - perfect for this task!
C and C++ can work together - use the best tool for the job
scanf needs & to get the variable's address
printf offers powerful format control
Smart programmers know when to borrow from other toolsets

🧠 Programming Wisdom

"When your knowledge base is limited to basic tools, don't be afraid to use related technologies that make your life easier. That's how real-world programming works!"

Examples

Sample Input 1:

Input:

23.0900

Sample Output 1:

Output:

23.09

Trailing zeros removed: 23.0900 → 23.09

Sample Input 2:

Input:

12.5200

Sample Output 2:

Output:

12.52

Trailing zeros removed: 12.5200 → 12.52

More Examples:

100.0 → 100 (decimal point removed too!)

0.00560 → 0.0056 (trailing zero removed)

3.14159 → 3.14159 (no trailing zeros to remove)

Solution.cpp

#include <cstdio>

int main() {
    double num;
    
    // scanf: C-style input
    // %lf = long float (double)
    // &num = address where to store the value
    scanf("%lf", &num);
    
    // printf with %g: Smart formatting!
    // - Removes trailing zeros automatically
    // - Removes trailing decimal if no fraction
    // - Uses shortest representation
    printf("%g\n", num);
    
    return 0;
}