what’s a vector ?
simply not precisely we can say that the vector is a Dynamic array of variables, struct or objects in which you Insert data at the end ; and this shows a Great difference with arrays in which arrays was created with a fixed size , this is simply why would we use a vector
declaring vectors :
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vector <int> myvector ; >> declaring an empty vector of integers
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vector <float > myvector (5) >> declaring a vector of floats having 5 spaces
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vector <int> myvector (10,1) >> declaring a vector of integers having 10 spaces all initialized with value 1
Accessing elements in a vectors :
we will focus on two ways to access elements inside the vector
the normal method ” indexing ” [] :
each element in the vector has an index beginning with index 0 for the first element 1 for the second and …etc till the final element and we use square brackets to write the index inside it
myvector[1] ; // to select the second element myvector[n-1] ; // to select the final element among n elements
the function at () :
the vector class has a member method called at() it takes the index of the element and returns the element having this element
myvector.at(1) ; // to index the second element in the vector
Are both the same ? :
actually no because in the first method no index range checking happens in the standard library’s vector so an access out of the array index bounds is not caught by the compiler for example
vector<int> myvector(5,1) ; cout<< myvector[6] ;
this might be caught by compiler as an error and might not , maybe rubbish is printed
(Range check- ing can be done by using at method ;
ie : myvector.at ( i ) is the same as a [ i ] , except that an exception is thrown if i is out-of-bounds
How to fill a vector :
myvector[5] = 13 ;
Inserting and Deleting Elements inside the vector :
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push_back() method is used to insert a new row in the vector // it takes the value of the row as an argument ex : myvector.push_back(15) ;
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pop_back() method is used to remove the last row in the vector
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Getting the size of a vector & changing it :
- size() method is used to return the size of the vector = the number of elements in the vector
- resize () takes two arguments the new size as and the value of the new added elements , if you didn’t add the second argument the new elements will have a value of zero by default
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