由于舍入，c 中的无限循环？

Question

以下代码无限循环。我相信这可能是一个四舍五入的问题，但并不完全确定。

我对 C 还很陌生，所以不确定为什么会出现无限循环。尽管不断循环，但代码似乎很有意义。

#include <stdio.h>
#include <cs50.h>
#include <math.h>
#include <string.h>



int main(void){

float quarter = .25;
int Qtr = 0;
float dime = .10;
int Dm = 0;
float nickel = .5;
int Nck = 0;
float penney = .01;
int Pn = 0;
float change;  
float userInput;
float newspaperCost;

do{
  printf("How much is the news paper today: \n");
  newspaperCost = GetFloat();
  printf("Amount Tendered: ");
  userInput = GetFloat();
  printf("You entered $%2.2f\n", userInput); 
  change = userInput - newspaperCost;
  printf("Change: $%2.2f\n", change); 
}

while(newspaperCost <= 0);

   while(change > 0){

  printf("%f\n", change);

  while(change - quarter > 0){

  change = change - quarter;
  Qtr++;

  }

  while(change - dime > 0){

  change = change - dime;
  Dm++;

  }

  while(change - nickel > 0){

  change = change - nickel;
  Nck++;

  }

  while(change - penney > 0){

  change = change - penney;
  Pn++;


  }

   } 

 printf("Your change consists of %d quarters, %d dimes, %d nickels, and %d pennies\n", Qtr, Dm, Nck, Pn);
   } //end main

Answer 1

不要使用浮点数来表示货币。
除非你有充分的理由，否则更喜欢双倍浮动。
便士*
您没有对浮点操作数使用任何相等运算符，因此您可能有逻辑错误。

Answer 2

您的代码：

do{
  printf("How much is the news paper today: \n");
  newspaperCost = GetFloat();
  printf("Amount Tendered: ");
  userInput = GetFloat();
  printf("You entered $%2.2f\n", userInput); 
  change = userInput - newspaperCost;
  printf("Change: $%2.2f\n", change); 
} while(newspaperCost <= 0);

不会在 newspaperCost <= 0 时退出此循环。我假设您没有在

输入负数

  printf("How much is the news paper today: \n");
  newspaperCost = GetFloat();

这就是为什么你有一个无限循环。

Answer 3

你在最后一个 while 循环中有一个逻辑错误。

而不是

while(change - penney > 0){
   change = change - penney;
   Pn++;
}

使用

while(change > 0){
   change = change - penney;
   Pn++;
}

由于舍入，c 中的无限循环？

Infinite loop in c due to rounding?

c

floating-point

infinite-loop

while-loop

cs50