我应该在括号之间写什么来定义我希望变量更改为的数据类型？

Question

If I have a variable as float var1 = 157.1; and want to transform it in int I would do int var2 = (int)var1;

I want to know about the other types of data, such as long int , short int , unsigned short int , long double and so on.

I tried long int var2 = (long int)var1; and it seemed to work, but I'm not sure if it is syntactically correct. If it is, I assume it'd be the same for all the other types, ie, just the data type and its attributes separated by a space. If it isn't I'd like to know if there's a list of them of some sort.

Answer 1

This is the C cast operator, but the operation is more generally "type casting", "casting", or "recasting". This is a directive to the compiler to request a specific conversion.

When casting any valid C type can be specified, so:

int x = 10;
unsigned long long y = (unsigned long long) x;

In many cases this conversion can be done implicitly, automatically, so it's not always necessary but in others you must force it. For example:

int x = 10;
float y = x; // Valid, int -> float happens automatically.

You can get caught by surprise though:

int x = 10;
float y = x / 3; // y = 3.0, not 3.333, since it does integer division before casting

Where you need to cast to get the right result:

int x = 10;
float y = (float) x / 3; // 3.33333...

Note that when using pointers this is a whole different game:

int x = 10;
int* px = &x;
float* y = (float*) px; // Invalid conversion, treats int as a float

Generally C trusts you to know what you're doing, so you can easily shoot yourself in the foot. What "compiles" is syntactically valid by definition, but executing properly without crashing is a whole other concern. Anything not specified by the C "rule book" (C standard) is termed undefined behaviour , so you'll need to be aware of when you're breaking the rules, like in that last example.

Sometimes breaking the rules is necessary, like the Fast Inverse Square Root which relies on the ability of C to arbitrarily recast values.