Round About

Problem

Read a floating point number from input, round it to the nearest integer, and print the result.

9. Round about, Comet 64

Solution 1

This solution exploits how floating point numbers are represented and handled in the Comet 64 computer. The computer allows for up to two decimal digits following the decimal point. If a floating point number cannot fit in the representation used by the computer, then the third decimal digit is rounded. The rounding rule is rounding half up. For example, the number 1.123 is rounded to 1.12 and 1.125 is rounded to 1.13. To round an input number to the nearest integer, we divide the input by 100 so the computer would round the result to two decimal places. Then multiply the rounded number by 100 to obtain the rounded integer. This solution is optimal, according to the game.

reg = input / 100;  // Divide by 100 to trigger rounding.
int = reg * 100;    // Multiply by 100 to get rounded integer.
output = int;       // Print the rounded integer.

Solution 2

We are rounding half up, i.e. round half toward positive infinity. Define our rounding function as

round(x) := floor(x + 0.5)

where we use the floor() function. The floor(x) function of a floating point number x is equivalent to the integer part of x. This solution is optimal, according to the game.

int = input + 0.5;  // The floor(x + 0.5) function.
output = int;       // Print the rounded integer.