#include<stdio.h>
#include<math.h>

bool Check(float P, float Vf, float Vin)
{
    float diff = Vf-Vin;

    if(diff<0)
        diff *= -1;

    if(diff<P)
        return 0;

    return 1;
}

float CalcVolt(float Vin, float R1, float R2, float C, int t)
{
    float Vout;

    Vout = float(Vin * (R2/(R1+R2)) * (1 - exp (-t * (R1+R2)/(C*R1*R2))));

    return Vout;
}

void Voltage(float Vin, float Vf, float R1, float R2, float C, int t, float Percentage)
{
    float Vout;

    int i = 0;

    do
    {
        Vout = CalcVolt(Vin, R1, R2, C, i*t);
        i += t;

        printf("At t = %3d : Vout = %5.3f Volts\n", i*t, Vout);
    }
    while(Check(Percentage, Vf, Vout));
}

int main()
{
    float Vf, Vin, R1, R2, C;
    float Percentage[3] = {0.1f, 0.05f, 0.01f};
    int choice;
    int t;

    printf("Enter Value of Vin: ");
    scanf("%f", &Vin);

    printf("Enter Value of R1: ");
    scanf("%f", &R1);

    while(R1<0)
    {
        printf("Negative value not allowed. Enter again. ");
        scanf("%f", &R1);
    }

    printf("Enter Value of R2: ");
    scanf("%f", &R2);

    while(R2<0)
    {
        printf("Negative value not allowed. Enter again. ");
        scanf("%f", &R2);
    }

    printf("Enter Value of Capacitor: ");
    scanf("%f", &C);
    
    while(C<0)
    {
        printf("Negative value not allowed. Enter again: ");
        scanf("%f", &C);
    }

    printf("Enter Value of t (time increment): ");
    scanf("%d", &t);

    while(t<0)
    {
        printf("Negative value not allowed. Enter again: ");
        scanf("%d", &t);
    }

    printf("Enter Value of Vf (final Voltage): ");
    scanf("%f", &Vf);

    printf("\nEnter 1 for 10%% of final value\n");
    printf("Enter 2 for  5%% of final value\n");
    printf("Enter 3 for  1%% of final value\n");
    printf("Percentage : ");
    scanf("%d", &choice);

    while(choice<1 || choice>3)
    {
        printf("Invalid choice, Enter again: ");
        scanf("%d", &choice);
    }

    printf("\n");

    Voltage(Vin, Vf, R1, R2, C, t, Percentage[choice-1]);

    return 0;
}

#include <time.h>
/*
* function declaration
*/
long t = time(0);
while(/*some condition here*/)
{
    if (time(0) > t)
    {
        printf("stuff\n");
        t = time(0);
    }
}