在 C++ 中的合并排序中传递数组时出错

Question

I am trying to implement a merge sort algorithm in c++ but I keep getting a compilation error which I am to unable to overcome.

Here is the code

#include <bits/stdc++.h>
using namespace std;

void sort(int a[],int l,int r,int b[]){

    int mid=(l+r)/2;
    int L[mid-l],R[r-mid];
    if((r-l)==1)
    b[0]=a[l];
    else if((r-l)>1){

        sort(a,l,mid,L);
        sort(a,mid,r,R);
        merge(L,(mid-l),R,(r-mid),b);
    }

    return;
}

void merge(int a[],int n,int b[],int m,int c[]){

    int i=0,j=0,k=0;
    while(k<(m+n)){
        if(j==m||(a[i]<=b[j]&&i<n)){
            c[k]=a[i];
            i++;
            k++;
        }
        else if(i==n||(b[j]<a[i]&&j<m)){
            c[k]=b[j];
            j++;  
            k++;
        }
    }

    return;
}

int main(){

    int n;
    cin>>n;
    int a[n],b[n];
    int i;
    for(i=0;i<n;i++){
        cin>>a[i];
    }
    sort(a,0,n,b);
    for(i=0;i<n;i++){
        cout<<b[i]<<" ";
    }
    return 0;
}

The error I keep getting is that I can't pass the array b[] from sort function to merge function.

Please help me correct the problem. Thanks in advance.

Answer 1

You need to declare merge before calling it. That means, you need to declare it before sort . For example -

void merge(int a[],int n,int b[],int m,int c[]);

Write this declaration before the definition of sort

EDIT I just figured out another error in this line

int a[n],b[n]

You cannot do this. In C++ the size of array must be a compile time constant.