Working on Code For Tank

We have been working on code that will have the tank drive and use the ultrasonic sensor to see things in front of it so it makes a turn until there ins't anything in front.

This is a piece of our code:

void stopm(void);
void forward(void);
void inputs(void);
void sharpright(void);

int duration;
float distance;

void setup(void)
{
  Serial.begin (9600);
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(IN1 ,OUTPUT);
  pinMode(IN2,OUTPUT);
  pinMode(IN3,OUTPUT);
  pinMode(IN4,OUTPUT);
  pinMode(ENA,OUTPUT);
  pinMode(ENB,OUTPUT);
  digitalWrite(ENA,HIGH);
  digitalWrite(ENB,HIGH);
 }