使用科学计数法定义常量导致Hackerearth题目报错的原因咨询

Ah, I see the issue here—you've got a simple but critical misunderstanding of how scientific notation works in C++! Let's break it down:

The core problem is what 10e9 actually represents. You probably intended it to mean 10^9 (which is 1,000,000,000), but in C++ (and most programming languages), 10e9 translates to 10 * 10^9—that's 10,000,000,000. So when you write 10e9+7, you're setting MOD to 10,000,000,007 instead of the required 1,000,000,007. That's a 10x difference, which explains why all your modulo operations are producing incorrect results.

Let's list out the key points to clarify:

• Correct scientific notation for 1e9+7: If you want to use scientific notation, you should write 1e9+7 (not 10e9+7). 1e9 is exactly 10^9, so adding 7 gives you the correct modulus value.
• Avoid floating point pitfalls: 10e9 is a floating-point constant, not an integer. While in this case converting it to long int might not lose precision, relying on floating-point numbers for integer constants is risky—for larger values, you could run into precision errors that mangle your integer values. Using the direct integer literal 1000000007 is always safer in programming contests.

Here's the fixed line of code you need:

const long int MOD = 1e9+7;
// Or, even better to avoid any confusion:
// const long int MOD = 1000000007;

Just swapping that line will get your code working as expected again. Remember, when dealing with modulus values in contests, double-check your literal values—small typos like this can derail an otherwise correct solution!

内容的提问来源于stack exchange，提问作者Ravi Soni