Программа для решение нелинейных уравнений

#include <stdio.h>
#include <math.h>
 
 double x, t, a, b, e, poh, delt; 
 
 double (*pfpr) (double, double);
 
 int m, s;
 char c;
 double z;
 
  
 double func1(double x, double t);
 double func2(double x, double t);
 double pol(double a, double b, double e);
 
 main(void) 
 {
    do
 {
   printf ("ENTER T: ");
   
   A:
    while (scanf("%lf%c", &t, &c)!=2||c!='\n')
    {
        printf ("DON'T USE SYMBOLS IN T. TRY AGAIN: ");
        fflush (stdin);
    }
    
    if (fabs(t)>=1000)
    {
        printf ("B IS TOO BIG (SMALL). TRY AGAIN: ");
        goto A;
    }
   
   Q:
   printf ("ENTER A (STARTING POINT): ");
   
   C:
   
   while (scanf("%lf%c", &a, &c)!=2||c!='\n')
    {
        printf ("DON'T USE SYMBOLS IN A. TRY AGAIN: ");
        fflush (stdin);
    }
    
    if (fabs(a)>=1000)
    {
        printf ("A IS TOO BIG (SMALL). TRY AGAIN: ");
        goto C;
    }
    
    
   printf ("ENTER B (ENDING POINT): ");
   
   D:
    while (scanf("%lf%c", &b, &c)!=2||c!='\n')
    {
        printf ("DON'T USE SYMBOLS IN B. TRY AGAIN: ");
        fflush (stdin);
    }
    
    if (fabs(b)>=1000)
    {
        printf ("B IS TOO BIG (SMALL). TRY AGAIN: ");
        goto D;
    }
   
   if (a>b)
   {
    printf ("B>A. TRY AGAIN: ");
    goto Q;
   }
   
   printf ("ENTER ACCURACY:\n");
    
    B:
    while (scanf("%lf%c", &e, &c)!=2||c!='\n')
    {
        printf ("DON'T USE SYMBOLS IN B. TRY AGAIN: ");
        fflush (stdin);
    }
    
    if (e>=1||e<1E-17)
    {
        printf ("B IS TOO BIG (SMALL). TRY AGAIN: ");
        goto B;
   }
   
   printf ("WHICH EQUATION DO YOU WANT TO COUNT? PRESS 1 UF THE FIRST PRESS 2 IF THE SECOND: ");
   
   while(scanf("%d%c", &m,&c)!=2||c!='\n'||m!=2&&m!=1)
{
    printf ("DON'T USE OTHER SYMBOLS IN THE MASSIVE. TRY AGAIN: ");
    fflush (stdin);
}
  
  printf ("WHICH WAY DO YOU WANT TO COUNT? PRESS 1 UF THE FIRST PRESS 2 IF THE SECOND: ");
  
   while(scanf("%d%c", &s,&c)!=2||c!='\n'||s!=2&&s!=1)
{
    printf ("DON'T USE OTHER SYMBOLS IN THE MASSIVE. TRY AGAIN: ");
    fflush (stdin);
}
 
 
 if (m==1)
    pfpr = func1;
   
 if (m==2)
    pfpr = func2;
 
  if (s==1)
  printf("X = %lf\n", pol(a, b, e));
 
  if (s==2)//метод ньютона
  {  
    x = b;
    
    z = 1e-15;  
  do 
{
    double q;
    q=pfpr(x+z, t);
    poh =(q-pfpr(x, t))/z;//ищем производную
     
    delt = pfpr(x,t)/poh;
    x- = delt;
       
    }while(delt>e);
    
 
    printf("poh = %lf\n", poh);
 }
 
 
   printf ("\nPRESS ESC TO EXIT. PRESS ANY KEY TO CONTINUE.\n");
   
} while (getch()!=27);
 }
 
 double pol(double a, double b, double e) //метод половинного деления
 {
    
    while (fabs (b - a)> e) 
   {
      x = (a + b) / 2;
      if (pfpr(a, t) *  pfpr(x, t)> 0)
         a = x;
      else
         b = x;
   }
   return x;
 }
 
 double func1(double x, double t)
 { 
   return (cos(t/x)-2*sin(1/x)+(1/x));
 }
 
 double func2(double x, double t)
 { 
   return (sin(log(x))-cos(log(x))+t*(log(x)));
 }