string - C's strtod() returns wrong values -

i'm working on banking terminal program laboratory exercises @ university.

what puts me off stride function supposed take user's input of amount transfered, check if fits requirements , if so, returns value provided program.

our tutor mad means of securing input, , have call error on kind of inconsistency. value high? error. negative or 0 value? error. number more precise 0.01? error. non-digit-non-dot characters in input? error.

due that, function definately overcomplicated, yet i'm fine that. drives me wall fact, both atof() , strtod() functions reads numbers in somehow wrong way.

long double take_amount() {     char input[21];     bool success, correct;     unsigned long int control1;     long double amount, control, control2, control3;          {         success = true, correct = true;         printf("\t\tamount:\t\t");         success = scanf("%20[^ \t\n]c", input);        __fpurge(stdin);          correct = check(input, 'b');          amount = strtod(input, null);          printf("\n\tgot %.20lf\n", amount); ///          control = amount * 100;         control1 = (unsigned long int)floor(control);         control2 = (long double) control1;         control3 = control2 - control;              printf("\n\tgot2 %.20lf\n", control3);  ///          if (control3 != 0)         {             if (control3 >= 1 || control3 <= -1)             {                 printf("\n\t\twe sorry, safety reasons impossible transfer");                 printf("\n\t\tsuch great amounts while online. if wish finalize");                 printf("\n\t\tthis operation, please, visit closest division of our bank.");                 printf("\n\t\twe sory inconvenience , wish pleasent day.");                 press_enter();              }             correct = false;             printf("\ndamn\n");     ///                 }          if (amount <= 0)         {             correct = false;             printf("\ngod damn\n");      ///         }          if(success == false || correct == false)         {             printf("\n\t\tinvalid input, please try again.\n\n");         }         else         {             printf("\t\t\t\t%.2lf\n", amount);             printf("\n\t\tis correct input? ((y)es/(n)o/(e)xit)");             if (accept())             {                 break;             }             else             {                 continue;             }             break;         }     }while (1);     return amount; 

as far functions used here goes, check() checks if string contains legal characters (digits , dot), press_enter() waits enter-press leave main menu , accept() reads y/n/e, return true on y, false on n , leaves menu on e.

the lengthy part control variables solution checking if number not more precise 0.01. sadly, doesn't work due strtod().

my problem strtod() doesn't work! medicore numbers, being far underflow or overflow, value returned doesn't match input. examples:

     enter amount deposit.         amount:     1234.45      got 1234.45000000000004547474      enter amount deposit.         amount:     0.999      got 0.99899999999999999911 

it not unlikely it's fault, after several hours code still couldn't come working solution , that's why i'm asking help, vise internauts of stack overflow.

is there way fix reading of strtod()? if not, there way take input let's me check needs checked?

edit: attention, please!

if haven't stated already, tutor not easiest guy work with, now.
forces use double format hold balance stored on accounts. know because 1 of collegues got program rejected using two-int, dollar - cent construction.

i highly appreciate here, can somehow solve problem? have use double type store money. have check if there no letters in input (scanf() set on %lf cut non-digits end), have check if input not more precise 0.01, have accept xxx.xx structure of input. suggestions?

use strtol read dollars , again (or own trivial function) read cents, combine them cents += 100*dollars; not use floating point currency. ever.