Prime factorization

#include<iostream>
#include<vector>
#include<cmath>
#include<map>
#define SIZE 20
using namespace std;
void sieve();
bool a[SIZE];
vector<int>factor1;
vector<int>factor2;
map<int,int>map1,map2;
map<int,int>::iterator cur;
main(){
    sieve();
    int i,m,c,b;
    cin>>c>>b;
    if(c<b){
    m=c;
    c=b;
    b=m;}

    i=2;
    while(i<=c){
    if(a[i]==0&&c%i==0)
    factor1.push_back(i);
    i++;}
    i=2;
    while(i<=b){
        if(a[i]==0&&b%i==0)
    factor2.push_back(i);
    i++;
    }
    for(i=0;i<factor1.size();i++)
    map1[factor1[i]]++;
    //cout<<factor1[i]<<" ";
    cout<<"\n";
    for(i=0;i<factor2.size();i++)
    map2[factor2[i]]++;
   // cout<<factor2[i]<<" ";
    for(cur=map1.begin();cur!=map1.end();cur++)
    cout<<cur->first<<" "<<cur->second;
    //if(map1[i]<map2[i])



}
void sieve(){
 int i,k;
 int sq=sqrt(SIZE);
 for(i=0;i<=SIZE;i++)
  a[i]=0;
 a[0]=a[1]=1;
  for(i=4;i<=SIZE;i+=2)
     a[i]=1;
  for(i=3;i<=sq;i++)
   if(a[i]==0)
   for(k=2*i;k<=SIZE;k+=i)
      a[k]=1;
      }