Computation Loop and duplicate entry error

I'm stuck! Here is problem I am having: The loop I have made calculates values based off an integer value entered by the user from the keyboard where if they enter the same value from a given interval a warning message is displayed followed by a return to the beginning of the loop.

Here is my code so far:

Code:

#include <stdio.h>

#include <math.h>

int main(void)

{

int x;

double A, B, C, f1, f2, f3;

printf("Enter a value for A, B, and C:\n");

scanf("%lf %lf %lf", &A, &B, &C);

printf("A = %g \tB = %g \tC = %g\n", A, B, C);

printf("Enter a value for x:\n");

scanf("%d", &x);

printf("x = %d\n",x);

if(x<=0){

printf("Case 1\n");

f1 = (A * pow(x, 3)) - (B * pow(x, 2)) + (x / 1.25);

printf("Value of x = %3d and y = %6.2f\n", x, f1);

}

else if(0<x<1){

printf("Case 2\n");

f2 = A * x - B * pow(x, 4) + pow(C, 2);

printf("Value of x = %3d and y = %6.2f\n", x, f2);

}

else if(x>=1){

printf("Case 3\n");

f3 = A * log(x) - B / x - 2 * A;

printf("Value of x = %3d and y = %6.2f\n", x, f3);

}

}

Very simple and basic code, as this is my first C/C++ class. The loop works great but I don't know where to go from here to create the additional inputs with the warning message and return to the beginning of the loop.

i hope what I am saying is making sense, I am going on about 4 hours sleep and being up for almost 20 hours at this point (gotta love being a student!).

Any help would be greatly appreciated.

-Dan