Expected primary-expression before ‘]’ token(bisection search)

Question

Where have I gone wrong in this? When I compile this ~

bs_01.cpp: In function ‘int main()’: bs_01.cpp:29:25: error: expected primary-expression before ‘]’ token cout << bisection_01(foo[]);

#include"std_lib_facilities.h"
using namespace std;

template <class T>
void bisection_01(T foo[])
{
    int low, high,mid;
    low = 0;
    high = (foo.size()-1);
    mid = (high+low)/2;
    while(low!=high)
    {
        if  (foo[mid]==0)
            if (foo[mid+1]==0)
                low = mid;
            else
                cout<<"The change has occured from "<<mid+1<<" to "<<mid+2;
        if (foo[mid]==1)
            if(foo[mid-1]==1)
                high = mid;
            else
                cout<<"The change has occured from "<<mid<<" to "<<mid+1;
    }
}

int main()
{
    int foo[7] {0, 0, 0, 0, 1, 1, 1};
    cout<<bisection_01(foo[]);
}

score 1 · Accepted Answer · answered Oct 07 '18 at 19:12

You can't pass foo[] to a function. Also bisection_01() returns void which can not be inserted into an ostream;

This code compiles and seems to do what you want:

#include <iostream>
#include <array>
using namespace std;

template <class T, size_t size>
void bisection_01(std::array<T,size> foo)
{
    int low, high,mid;
    low = 0;
    high = (size-1);
    mid = (high+low)/2;
    while(low!=high)
    {
        if  (foo[mid]==0) {
            if (foo[mid + 1] == 0)
                low = mid;
            else
                std::cout << "The change has occured from " << mid + 1 << " to " << mid + 2;
        }
        if (foo[mid]==1) {
            if (foo[mid - 1] == 1)
                high = mid;
            else
                std::cout << "The change has occured from " << mid << " to " << mid + 1;
        }
    }
}

int main()
{
    std::array<int,7> foo{0, 0, 0, 0, 1, 1, 1};
    bisection_01(foo);
}

Expected primary-expression before ‘]’ token(bisection search)

1 Answers1