How to perform A-B set operation in C program using builtin library

I am new to C language. Suppose I have two arrays a and b

int a[10] = { 1,2,3,4,5,6,7,8,9,0 };
int b[10] = { 1,3,5,7,9 };

and I want to perform a-b so that I can get all elements of array a which are not present in array b. In ruby or python, I can just simply do a-b and get the result. Here is my c code that I have tried but my code which is not working.I am looking for a C library that does this operation for me in a line.I have also found this library but not sure how to implement it. Any kind of help is appreciated.

#include<stdio.h>
#define Max 100

int m,n,i,j,k,p,q,r,s;
int flag=1;
char char1,char2,char3;
void Difference(int *,int *,int ,int);
void Display2(char ,char ,int );

int a[10] = { 1,2,3,4,5,6,7,8,9,0 };
int b[10] = { 1,3,5,7,9 };
int c[10];

void Difference(int *a1,int *b1,int m1,int n1)
{
    q=0;
    p=0;
    i=0;
    for(k=0;k<m1;k++){
        flag=1;
        for(j=0;j<n1;j++){
            if(b1[j]==a1[k]){
                flag=1;
                q++;
                break;
            }
            else{
                flag=0;
            }
        }
        if(flag==0){
            c[p]=a1[k];
            p++;
        }
    }
}

void Display2(char ac,char bc,int m1)
{
    printf("\nThe Difference Of Two Sets i.e '%c - %c' Is : { ",ac,bc);
    r = m1 - q;
    for(p=0;p<r;p++){
        printf("%2d",c[p]);
    }
    printf(" }");
}


int main(){
    Difference(a,b,m,n);
    Display2('A','B',m);
    return 0;
}

I can guess, you forgot to initialize your m and n variables with proper values. Add m = 10; n = 5; before calling Difference and your code will work.

I also suggest you to write more readable code: better naming for variables, use some spaces and avoid global variables.

Edit: In C++ you can write:

#include <algorithm>
#include <iostream>
#include <iterator>
#include <set>

int main() {
    std::set<int> a = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    std::set<int> b = { 1, 3, 5, 7, 9 };
    std::set<int> c;

    std::set_difference(a.begin(), a.end(), b.begin(), b.end(), std::inserter(c, c.begin()));

    for (const auto item : c) 
        std::cout << item << " ";

    return 0;
} 

Detail information about std::set_difference can be found here