Question

i want to implement binary_search with pointers

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

int binary_p(int x[],int size,int target){
    int *p=&x[0];
    int *q=&x[size];

    while(p<q){
               int mid=(p+q)>>2;
               if (target==x[*mid]) return 1;
               else if(target<x[*mid])  q=mid-1;
               else p=mid+1;





               }   
    return -1;


}
int main(int argc, char *argv[])
{
    int x[]={2,4,6,7,9,10,12};
    int size=sizeof(x)/sizeof(int);
    int target=9;
    cout<<binary_p(x,size,target)<<endl;
    system("PAUSE");
    return EXIT_SUCCESS;
}

but here is error list

  prog.cpp: In function ‘int binary_p(int*, int, int)’:
prog.cpp:10: error: invalid operands of types ‘int*’ and ‘int*’ to binary ‘operator+’
prog.cpp:11: error: invalid type argument of ‘unary *’
prog.cpp:12: error: invalid operands of types ‘int*’ and ‘int’ to binary ‘operator*’
prog.cpp:12: error: invalid conversion from ‘int’ to ‘int*’
prog.cpp:13: error: invalid conversion from ‘int’ to ‘int*’
prog.cpp: In function ‘int main(int, char**)’:
prog.cpp:30: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result

please could anybody give me advise

Answer 1

Here is the working code.

#include <cstdlib>
#include <iostream>

using namespace std;

int binary_p(int x[],int size,int target){
    int *p = &x[0];
    int *q = &x[size - 1 ];

    while( *p < *q ){
        int mid = (*p + *q) >> 2;
        if (target == x[mid]) 
            return 1;
        else if (target < x[mid])  
            *q = mid - 1;
        else 
            *p = mid + 1;
    }   
    return -1;
}
int main(int argc, char *argv[])
{
    int x[] = {2,4,6,7,9,10,12};
    int size = sizeof(x) / sizeof(int);
    int target = 9;
    cout << binary_p(x,size,target) << endl;
    //system("PAUSE");
    return EXIT_SUCCESS;
}