Iterate through the vector comparing each element with all elements after it; if at any point they are equal, then the vector contains two numbers that are equal. If you make it through without that happening, then all the elements are distinct.
To do Zhuge's suggestion, all you need to do is something like this:
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for(i = 0;i < yourvectorname.size();++i)
for(j = i + 1;j < yourvectorname.size();++j)
if(yourvectorname.at(i) == yourvectorname.at(j))
std::cout << "Two elements with the same value found at " << i << " and " << j << "!\n";
A more pressing issue here is that you are NOT USING ANY VECTORS IN YOUR CODE ANYWHERE!