How to check duplicate number in arrays in C language

here's the code in C language

#include<stdio.h>

int main()

{

    int array[6]={1,2,5,3,4};

    int a,b;

    for(a=0;a<5;a++)

    {

        b=1;

        while(array[a]==array[a+b])

        {

            b++;

            break;

        }

        if(b>1)break;

    }

    if(b==1)printf("no duplicate number in that array");

    else if(b>1)printf("have duplicate number in that array");

    return 0;

}

that is all from me 

thank you