🧮 Why Does C Print 0.300000 for 0.1 + 0.2?

This short example shows how floating-point numbers behave in C and why simple expressions like 0.1 + 0.2 don't always behave as you'd expect.

🔢 Code: `test.c`

#include <stdio.h>

int main () {
    printf("%f\n", 0.1 + 0.2);        // Default format: 6 digits after decimal
    printf("%.17f\n", 0.1 + 0.2);     // Full precision for a double
}

💻 Output

0.300000
0.30000000000000004

🧠 What's Going On?

Floating-point numbers are approximations

C uses the IEEE 754 standard to represent floating-point numbers (float, double).

Some numbers like 0.5 are exact in binary.
But others like 0.1 or 0.2 cannot be exactly represented.

So when you write:

0.1 + 0.2

You're actually adding:

0.10000000000000000555... + 0.20000000000000001110...

Which gives:

0.30000000000000004441...

This is not exactly 0.3, though it's very close.

🖨️ Why the different outputs?

By default, `printf("%f", ...)` prints only 6 digits after the decimal

Format String	Meaning	Output
`%f`	6 digits (default)	`0.300000`
`%.17f`	17 digits = full double	`0.30000000000000004`

The value 0.30000000000000004 is rounded to 0.300000 when printed with %f.

📌 Takeaway for Students

Floating-point numbers are not exact.
Even simple decimal values like 0.1 and 0.2 can have invisible errors due to binary representation.
C (and most other languages) hides this by default, but you can reveal it using higher precision formats.
Always be careful when comparing floats or expecting exact decimal values in output.

✅ This is expected behavior, not a bug!

kayceesrk/floating_point_in_c.md