_PsychoKiller's blog

By _PsychoKiller, history, 3 months ago, In English,

#include<bits/stdc++.h> using namespace std; typedef long long LL ; vector <LL> v[100]; vector <LL> v1; int main(){ cout << v[1].size() - 1 << endl; //This gives output 4294967295 int sz = v[1].size() - 1; cout << sz << endl; //This gives output -1 LL sz1 = v[1].size() - 1; cout << sz1 << endl; //This gives output 4294967295 cout << v[1].size() << endl; //This gives output 0 cout << v1.size() - 1 << endl; //This gives output 4294967295 cout << v1.size() << endl; //This gives output 0 }

Can anyone give any explanation? I lost a lot of valuable time in the contests for these stuffs and I can't understand why.

 
 
 
 
  • Vote: I like it  
  • -7
  • Vote: I do not like it  

»
3 months ago, # |
  Vote: I like it +4 Vote: I do not like it

The vector's (and other standard data structures like stack, set, ...) .size() is of type unsigned int, which has limits of 0 to 232 - 1.

Like int (a normal int has its limits from  - 231 to 231 - 1), if you give it a value that exceeds its range, it will just cycle it around to a value that is in the range. For example, giving an unsigned int the value  - 10 would make it cycle up to 232 - 10.

So, when you give the unsigned the value  - 1, it becomes 4294967295, and then if you assign this value to an int it cycles the int down, and gets it to  - 1. If you assign this value to a long long type, no cycles occur because the value is inside long long's range.