struct _pid {
    int pv; /*integer that contains the process value*/
    int sp; /*integer that contains the set point*/
    float integral;
    float pgain;
    float igain;
    float dgain;
    int deadband;
    int last_error;
};
struct _pid warm, *pid;
int process_point, set_point, dead_band;
float p_gain, i_gain, d_gain, integral_val, new_integ;;
/*------------------------------------------------------------------------
pid_init
DESCRIPTION This function initializes the pointers in the _pid structure
to the process variable and the setpoint. *pv and *sp are
integer pointers.
------------------------------------------------------------------------*/
void pid_init(struct _pid *warm, int process_point, int set_point)
{
    struct _pid *pid;
    pid = warm;
    pid->pv = process_point;
    pid->sp = set_point;
}
/*------------------------------------------------------------------------
pid_tune
DESCRIPTION Sets the proportional gain (p_gain), integral gain (i_gain),
derivitive gain (d_gain), and the dead band (dead_band) of
a pid control structure _pid.
------------------------------------------------------------------------*/
void pid_tune(struct _pid *pid, float p_gain, float i_gain, float d_gain, int dead_band)
{
    pid->pgain = p_gain;
    pid->igain = i_gain;
    pid->dgain = d_gain;
    pid->deadband = dead_band;
    pid->integral = integral_val;
    pid->last_error = 0;
}
/*------------------------------------------------------------------------
pid_setinteg
DESCRIPTION Set a new value for the integral term of the pid equation.
This is useful for setting the initial output of the
pid controller at start up.
------------------------------------------------------------------------*/
void pid_setinteg(struct _pid *pid, float new_integ)
{
    pid->integral = new_integ;
    pid->last_error = 0;
}
/*------------------------------------------------------------------------
pid_bumpless
DESCRIPTION Bumpless transfer algorithim. When suddenly changing
setpoints, or when restarting the PID equation after an
extended pause, the derivative of the equation can cause
a bump in the controller output. This function will help
smooth out that bump. The process value in *pv should
be the updated just before this function is used.
------------------------------------------------------------------------*/
void pid_bumpless(struct _pid *pid)
{
    pid->last_error = (pid->sp) - (pid->pv);
}
/*------------------------------------------------------------------------
pid_calc
DESCRIPTION Performs PID calculations for the _pid structure *a.
This function uses the positional form of the pid equation,
and incorporates an integral windup prevention algorithim. Rectangular integration is used,
so this function must be repeated on a consistent time basis for accurate control.
RETURN VALUE The new output value for the pid loop.
USAGE #include "control.h"*/
float pid_calc(struct _pid *pid)
{
    int err;
    float pterm, dterm, result, ferror;
    err = (pid->sp) - (pid->pv);
    if (abs(err) > pid->deadband) {
        ferror = (float) err; /*do integer to float conversion only once*/
        pterm = pid->pgain * ferror;
        if (pterm > 100 || pterm < -100) {
            pid->integral = 0.0;
        }
        else {
            pid->integral += pid->igain * ferror;
            if (pid->integral > 100.0) {
                pid->integral = 100.0;
            }
            else if (pid->integral < 0.0) {
                pid->integral = 0.0;
            }
        }
        dterm = ((float)(err - pid->last_error)) * pid->dgain;
        result = pterm + pid->integral + dterm;
    }
    else {
        result = pid->integral;
    }
    pid->last_error = err;
    return (result);
}
void main(void)
{
    float display_value;
    int count = 0;
    pid = &warm;
// printf("Enter the values of Process point, Set point, P gain, I gain, D gain \n");
// scanf("%d%d%f%f%f", &process_point, &set_point, &p_gain, &i_gain, &d_gain);
    process_point = 30;
    set_point = 40;
    p_gain = (float)(5.2);
    i_gain = (float)(0.77);
    d_gain = (float)(0.18);
    dead_band = 2;
    integral_val = (float)(0.01);
    printf("The values of Process point, Set point, P gain, I gain, D gain \n");
    printf(" %6d %6d %4f %4f %4f\n", process_point, set_point, p_gain, i_gain, d_gain);
    printf("Enter the values of Process point\n");
    while (count <= 20) {
        scanf("%d", &process_point);
        pid_init(&warm, process_point, set_point);
        pid_tune(&warm, p_gain, i_gain, d_gain, dead_band);
        pid_setinteg(&warm, 0.0); //pid_setinteg(&warm,30.0);
//Get input value for process point
        pid_bumpless(&warm);
// how to display output
        display_value = pid_calc(&warm);
        printf("%f\n", display_value);
//printf("\n%f%f%f%f",warm.pv,warm.sp,warm.igain,warm.dgain);
        count++;
    }
}