in c++ expected primary expression before ']' - c++

Question

Here is my code for quick sort. I am a beginner kindly please help.
#include<iostream>
using namespace std;
class quick
{
private:
int n,left,right,i,j;
float a[55];
public:
void getdata();
void sort(float[],int,int);
void putdata();
};
void quick::getdata()
{
cout<<"Enter how many elements you want to enter:";
cin>>n;
for(int k=0;k<n;k++)
{
cout<<"Enter percentage of students:"<<k+1<<":";
cin>>a[k];
}
left=0;
right=n-1;
}
void quick::putdata()
{
for(int k=0;k<5;k++)
{
cout<<"\nSorted marks are:"<<a[k]<<endl;
}
}
void quick::sort(float a[],int left,int right)
{
if(left<right)
{
int i=left;
int j=right+1;
float pivot=a[left];
do{
do{
i++;
}while((a[i]<pivot)&& left<right);
do{
j--;
}while(a[j]>pivot);
if(i<j)
swap(a[i],a[j]);
}while(i<j);
a[left]=a[j];
a[j]=pivot;
sort(a,left,j-1);
sort(a,j+1,right);
}
}
int main()
{
quick obj;
obj.getdata();
obj.sort(a[],left,right);
obj.putdata();
return (0);
}
It is giving me error in int main() function:
a is not declared in this scope.
expected primary expression before ']'.

Answer 1

As the answer is given by #Shubham Khatri. Here is the corrected code.
#include<iostream>
using namespace std;
class quick
{
public: int n,left,right,i,j;
float a[55];
public:
void getdata();
void sort(float[],int,int);
void putdata();
};
void quick::getdata()
{
cout<<"Enter how many elements you want to enter:";
cin>>n;
for(int k=0;k<n;k++)
{
cout<<"Enter percentage of students:"<<k+1<<":";
cin>>a[k];
}
left=0;
right=n-1;
}
void quick::putdata()
{
for(int k=0;k<n;k++)
{
cout<<"\nSorted marks are:"<<a[k]<<endl;
}
}
void quick::sort(float a[],int left,int right)
{
if(left<right)
{
int i=left;
int j=right+1;
float pivot=a[left];
do{
do{
i++;
}while((a[i]<pivot)&& left<right);
do{
j--;
}while(a[j]>pivot);
if(i<j)
swap(a[i],a[j]);
}
while(i<j);
a[left]=a[j];
a[j]=pivot;
sort(a,left,j-1);
sort(a,j+1,right);
}
}
int main()
{
quick obj;
obj.getdata();
obj.sort(obj.a,obj.left,obj.right);
obj.putdata();
return (0);
}

Answer 2

As it mentions you have not declared a as a variable inside the int main(). Rather it is an object of quick. In a function you don't pass array like a[] rather as a only .since a, left, right are a private variable of a class you can't access it from the object directly. Declare it as public and use it as obj.a, obj.left, obj.right inside sort function.
Complete code:
#include<iostream>
using namespace std;
class quick
{
public:
int n,left,right,i,j;
float a[55];
void getdata();
void sort(float[],int,int);
void putdata();
};
void quick::getdata()
{
cout<<"Enter how many elements you want to enter:";
cin>>n;
for(int k=0;k<n;k++)
{
cout<<"Enter percentage of students:"<<k+1<<":";
cin>>a[k];
}
left=0;
right=n-1;
}
void quick::putdata()
{
for(int k=0;k<5;k++)
{
cout<<"\nSorted marks are:"<<a[k]<<endl;
}
}
void quick::sort(float a[],int left,int right)
{
if(left<right)
{
int i=left;
int j=right+1;
float pivot=a[left];
do{
do{
i++;
}while((a[i]<pivot)&& left<right);
do{
j--;
}while(a[j]>pivot);
if(i<j)
swap(a[i],a[j]);
}while(i<j);
a[left]=a[j];
a[j]=pivot;
sort(a,left,j-1);
sort(a,j+1,right);
}
}
int main()
{
quick obj;
obj.getdata();
obj.sort(obj.a,obj.left,obj.right);
obj.putdata();
return (0);
}