#include "Arduino.h"

class MotorShield
{
  public:
    MotorShield(uint8_t speedPinLeft, uint8_t dirPinLeft,
        uint8_t speedPinRight, uint8_t dirPinRight);
    void init();
    void forward();
    void backward();
    void stop();
    void fullSpeed();
    void stopLeft();
    void stopRight();
  private:
    uint8_t speedPinLeft,
            dirPinLeft,
            speedPinRight,
            dirPinRight,
            maxSpeed,
            minSpeed;
};

#include "Arduino.h"

class MotorShield
{
  public:
    MotorShield(uint8_t speedPinLeft, uint8_t dirPinLeft,
        uint8_t speedPinRight, uint8_t dirPinRight);
    void init();
    void forward();
    void backward();
    void stop();
    void fullSpeed();
    void stopLeft();
    void stopRight();
  private:
    int speedPinLeft,
        dirPinLeft,
        speedPinRight,
        dirPinRight,
        maxSpeed,
        minSpeed;
};

--- 
+++ 
@@ -13,10 +13,10 @@
     void stopLeft();
     void stopRight();
   private:
-    int speedPinLeft,
-        dirPinLeft,
-        speedPinRight,
-        dirPinRight,
-        maxSpeed,
-        minSpeed;
+    uint8_t speedPinLeft,
+            dirPinLeft,
+            speedPinRight,
+            dirPinRight,
+            maxSpeed,
+            minSpeed;
 };
Change var types to the same type that constructor expects
