It has nothing to do with the size of this number, but is determined by the data type.

"Is there anything that a digital computer can't figure out?"

Many digital computers can't calculate accurately, but can only estimate approximately, such as irrational numbers or partial trigonometric functions. Decimals with long mantissas are usually approximations.

"Why do integers occupy four words in C language?"

In fact, your statement is not correct. It should be said that in computer C language, integers account for 4 bytes. Traditionally, the word length of a 32-bit machine is 4 bytes, so the original integer is 4 bytes. The integer of 8/ 16 bit machine is 2 bytes, and the integer of 64 bit machine is 8 bytes.