Question

i have following code in c++

#include <iostream>
using namespace std;

void qsort5(int a[],int n){
    int i;
    int j;
    if (n<=1)
        return;
    for (i=1;i<n;i++)
        j=0;
    if (a[i]<a[0])
        swap(++j,i,a);
    swap(0,j,a);
    qsort5(a,j);
    qsort(a+j+1,n-j-1);
}

int main()
{
    return 0;
}

void swap(int i,int j,int a[])
{
    int t=a[i];
    a[i]=a[j];
    a[j]=t;
}

i have problem

1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(13) : error C2780: 'void std::swap(std::basic_string<_Elem,_Traits,_Alloc> &,std::basic_string<_Elem,_Traits,_Alloc> &)' : expects 2 arguments - 3 provided
1>        c:\program files\microsoft visual studio 9.0\vc\include\xstring(2203) : see declaration of 'std::swap'
1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(13) : error C2780: 'void std::swap(std::pair<_Ty1,_Ty2> &,std::pair<_Ty1,_Ty2> &)' : expects 2 arguments - 3 provided
1>        c:\program files\microsoft visual studio 9.0\vc\include\utility(76) : see declaration of 'std::swap'
1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(13) : error C2780: 'void std::swap(_Ty &,_Ty &)' : expects 2 arguments - 3 provided
1>        c:\program files\microsoft visual studio 9.0\vc\include\utility(16) : see declaration of 'std::swap'
1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(14) : error C2780: 'void std::swap(std::basic_string<_Elem,_Traits,_Alloc> &,std::basic_string<_Elem,_Traits,_Alloc> &)' : expects 2 arguments - 3 provided
1>        c:\program files\microsoft visual studio 9.0\vc\include\xstring(2203) : see declaration of 'std::swap'
1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(14) : error C2780: 'void std::swap(std::pair<_Ty1,_Ty2> &,std::pair<_Ty1,_Ty2> &)' : expects 2 arguments - 3 provided
1>        c:\program files\microsoft visual studio 9.0\vc\include\utility(76) : see declaration of 'std::swap'
1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(14) : error C2780: 'void std::swap(_Ty &,_Ty &)' : expects 2 arguments - 3 provided
1>        c:\program files\microsoft visual studio 9.0\vc\include\utility(16) : see declaration of 'std::swap'
1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(16) : error C2661: 'qsort' : no overloaded function takes 2 arguments
1>Build log was saved at "file://c:\Users\dato\Documents\Visual Studio 2008\Projects\qsort5\qsort5\Debug\BuildLog.htm"

please help

Answer 1

swap is a function in std which must be included by <iostream>. When you attempt to make calls to your swap, it can’t find it (I’ll explain in a moment) and instead looks at the std::sort, which takes two arguments (hence the first error).

The reason it can’t find your swap is because it is declared after it is called. You need to either move the definition of your swap above that of qsort5 or forward declare it:

void swap(int i,int j,int a[]);

void qsort5(int a[],int n){ 
  ...

That tells the compiler that your swap function exists and it will use that when you call swap with 3 arguments.