Converting Large Numbers

What happens if I try to convert a really big number to a smaller type?

When you try to convert a number that's too big for its destination type, you can run into problems. Let's look at some examples to understand what happens:

#include <iostream>
using namespace std;

int main() {
  // A really big number
  long long BigNumber{12345678901234};

  // Try to convert it to a regular int
  int SmallNumber{static_cast<int>(BigNumber)};  

  cout << "Original number: " << BigNumber;
  cout << "\nConverted number: " << SmallNumber;
}
Original number: 12345678901234
Converted number: 1942892530

When you run this program, you might get unexpected results - the number might be completely different from what you put in! This is called overflow, and it happens because different number types can hold different ranges of values.

Here's another example with decimal numbers:

#include <iostream>
using namespace std;

int main() {
  // A float can't hold as many decimal places
  // as a double
  double Precise{123456789.123456789};
  float LessPrecise{static_cast<float>(Precise)};  

  // Show more decimal places
  cout.precision(12);
  cout << "Original number: " << Precise;
  cout << "\nConverted number: " << LessPrecise;
}
Original number: 123456789.123
Converted number: 123456792

Notice how we lost some precision in the decimal places! This is because float can't store as many digits as double.

To avoid these problems, you should:

  • Use types that are big enough for your numbers
  • Test your conversions with the actual values you'll be using
  • Use uniform initialization with { } instead of = when possible, as it will warn you about dangerous conversions
  • Consider whether you really need to convert between types at all

Remember: just because C++ lets you convert between types doesn't always mean you should!

Implicit Conversions and Narrowing Casts

Going into more depth on what is happening when a variable is used as a different type

Questions & Answers

Answers are generated by AI models and may not have been reviewed. Be mindful when running any code on your device.

Testing Type Conversions
Is there a way to check what value a type will be converted to before using it?
Numbers as Booleans
Why does C++ treat non-zero numbers as true and zero as false?
Performance Impact
Are implicit conversions slower than using exact types?
Purpose of Implicit Conversions
Why do we need implicit conversions at all? Wouldn't it be safer to always require exact types?
Disabling Implicit Conversions
Can I prevent the compiler from doing any implicit conversions in my code?
Language Comparison
What's the difference between how C++ handles conversions versus other languages?
Memory Usage
How do implicit conversions affect memory usage in my program?
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