the book I learn from gave a task to write a program which gets a matrix , and we have to write a function that switches 2 columns or rows the user inputs .
this chapter still not covers the pointers subject . as far as I know a function can not change variables in the main function without using pointers .
so , theoretically, can a function described here can be written without using pointers ? as far as I tried - it can not . am I missing something here or the book's just wrong?
thank you!
Arrays are already passed to functions via a pointer (rather than copying the entire array) so there's nothing (extra) to be done here.
can you show a quick example or logic ?
There's nothing extra, so no example is necessary as you should already know it.
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
ok, so I'm writing here 2 version of the function - one calling the matrix (matrix [4][4]) and the other don't - why doesn't it work?
the second oneCode:int swich_col (int matrix,int col1,int col2) { int tmp[4]; for (int i=0;i<4;i++) tmp[i]=matrix[i][col1]; for (int i=0;i<4;i++) matrix[i][col1]=matrix[i][col2]; for (int i=0;i<4;i++) matrix[i][col2]=tmp[i]; }
the error I get is in the compilation is :Code:int swich_col (int col1,int col2) { int tmp[4]; for (int i=0;i<4;i++) tmp[i]=matrix[i][col1]; for (int i=0;i<4;i++) matrix[i][col1]=matrix[i][col2]; for (int i=0;i<4;i++) matrix[i][col2]=tmp[i]; }
[Error] invalid conversion from 'int (*)[4]' to 'int' [-fpermissive]
Notice that in your first version, matrix is declared as an int.
Look up a C++ Reference and learn How To Ask Questions The Smart Way
what should I write instead ? every other try gives me different error..
(btw , the matrix does only get integer as values, why is it an error?)
I would expect something like:
Code:int switch_col(int matrix[4][4], int col1, int col2)You are trying to pass an array of arrays of ints as an argument when the corresponding parameter is an int. The matrix is not an integer, so of course it is an error.
Look up a C++ Reference and learn How To Ask Questions The Smart Way
it works! thank you very much!
so in conclusion , in order to incorporate array/matrix in a function you have to call it as: <the type of vars inside the array> <the name of the array> <[a1][a2][a3][]...[][an]> (the number of dimensions of the array) ?
Not quite, in order to incorporate array/matrix in a function, you may define and/or declare it as: <the type of vars inside the array> <the name of the array> <[a1][a2][a3][]...[][an]> (the number of dimensions of the array). When you call it, you just pass the <the name of the array> as the corresponding parameter. There are also ways to define and/or declare a function which has a matrix as a parameter using pointer syntax.
Do you understand the difference among define, declare, and call yet? You "define" a function when you write it. You "declare" a function when you supply a function prototype usually before the definition. The definition also serves as a declaration if definition comes before all uses of that function. You call a function when you use or execute it in another function.
Last edited by pheininger; 01-17-2014 at 02:16 PM. Reason: minor grammar correction then added the commenct about pointer syntax.
