diff --git a/10.4 b/10.4
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Binary files /dev/null and b/10.4 differ
diff --git a/10.4.cpp b/10.4.cpp
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+++ b/10.4.cpp
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+#include <iostream>
+using namespace std;
+
+const int INF = ~(1<<31);
+
+void swap(int &a, int &b){
+    a = a^b;
+    b = a^b;
+    a = a^b;
+}
+int flipsign(int a){
+    int d = a < 0 ? 1 : -1;
+    int opa = 0;
+    while(a != 0){
+        a += d;
+        opa += d;
+    }
+    return opa;
+}
+int abs(int a){
+    if(a < 0) a = flipsign(a);
+    return a;
+}
+bool opsign(int a, int b){
+    return (a>0 && b<0) || (a<0 && b>0);
+}
+int times(int a, int b){
+    int aa = abs(a), bb = abs(b);
+    int res = 0;
+    if(aa < bb) swap(aa, bb);
+    for(int i=0; i<bb; ++i, res += aa);
+    if(opsign(a, b)) res = flipsign(res);
+    return res;
+}
+int minuss(int a, int b){
+    return a + flipsign(b);
+}
+int divide(int a, int b){
+    if(b == 0) return INF;
+    int aa = abs(a), bb = abs(b);
+    int res = 0;
+    for(; (aa -= bb)>=0; ++res);
+    if(opsign(a, b)) res = flipsign(res);
+    return res;
+}
+int main(){
+    int a[] = {
+        8, 0, -8, -5, 9
+    };
+    int b[] = {
+        3, 5, 3, 0, -3
+    };
+    for(int i=0; i<5; ++i){
+        cout<<times(a[i], b[i])<<" "<<minuss(a[i], b[i])<<" "<<divide(a[i], b[i])<<endl;
+    }
+    return 0;
+}
diff --git a/10.6 b/10.6
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Binary files /dev/null and b/10.6 differ
diff --git a/10.6.cpp b/10.6.cpp
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--- /dev/null
+++ b/10.6.cpp
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+#include <iostream>
+#include <map>
+#include <cmath>
+#include <cstdlib>
+#include <ctime>
+using namespace std;
+
+struct point{
+    double x, y;
+};
+class line{
+public:
+    double epsilon, slope, intercept;
+    bool bslope;
+public:
+    line(){}
+    line(point p, point q){
+        epsilon = 0.0001;
+        if(abs(p.x - q.x) > epsilon){
+            slope = (p.y-q.y) / (p.x-q.x);
+            intercept = p.y - slope * p.x;
+            bslope = true;
+        }
+        else{
+            bslope = false;
+            intercept = p.x;
+        }
+    }
+    void print(){
+        cout<<"y = "<<slope<<"x + "<<intercept<<endl;
+    }
+};
+
+bool operator <(const line &l1, const line &l2){
+    return l1.slope < l2.slope;
+}
+bool equal(double a, double b){
+    return abs(a-b) < 0.0001;
+}
+bool operator ==(const line &l1, const line &l2){
+    if(l1.bslope == l2.bslope && equal(l1.slope, l2.slope) && equal(l1.intercept, l2.intercept))
+            return true;
+        return false;
+}
+line find_best_line(point *p, int point_num){
+    line bestline;
+    bool first = true;
+    map<line, int> line_count;
+    for(int i=0; i<point_num; ++i){
+        for(int j=i+1; j<point_num; ++j){
+            line l(p[i], p[j]);
+            if(line_count.find(l)==line_count.end())
+                line_count[l] = 0;
+            line_count[l] = line_count[l] + 1;
+            if(first){
+                bestline = l;
+                first = false;
+            }
+            else{
+                if(line_count[l] > line_count[bestline])
+                    bestline = l;
+            }
+        }
+    }
+    cout<<line_count[bestline]<<endl;
+    return bestline;
+}
+int main(){
+    srand((unsigned)time(0));
+    int graph_size = 10;
+    int point_num = 500;
+    point *p = new point[point_num];
+    for(int i=0; i<point_num; ++i){
+        p[i].x = rand()/double(RAND_MAX) * graph_size;
+        p[i].y = rand()/double(RAND_MAX) * graph_size;
+        cout<<p[i].x<<" "<<p[i].y<<endl;
+    }
+    line l = find_best_line(p, point_num);
+    l.print();
+    return 0;
+}