In cs5's week 2 hours practice problem, the code correctly gives the total hours spent, but it truncates the average hours per week despite using float. Where am I going wrong?

在中五的S周两小时练习题中，代码正确地给出了总课时，但尽管使用了浮动，它还是截断了每周的平均课时。我哪里错了？

#include <cs50.h>
#include <ctype.h>
#include <stdio.h>

float calc_hours(int hours[], int weeks, char output);

int main(void)
{
    int weeks = get_int("Number of weeks taking CS50: ");
    int hours[weeks];

    for (int i = 0; i < weeks; i++)
    {
        hours[i] = get_int("Week %i HW Hours: ", i);
    }

    char output;
    do
    {
        output = toupper(get_char("Enter T for total hours, A for average hours per week: "));
    }
    while (output != 'T' && output != 'A');

    printf("%.1f hours\n", calc_hours(hours, weeks, output));
}

// TODO: complete the calc_hours function
float calc_hours(int hours[], int weeks, char output)
{
 int tot = 0;

     for (int i = 0; i < weeks; i++)
    {
            tot = hours[i] + tot;
    }

    if (output == 'T')
    {
        return (float) tot;
    }
    return (float) (tot / weeks);
}

I typed in the weeks and hours spent per week when prompted and typed in A to get average of hours spent per week, but it only outputs an integer value instead of a float.

当出现提示并输入A时，我输入了每周花费的周和小时数，但它只输出一个整数值，而不是浮点数。

Problem:

问题：

(float) (tot / weeks)

"Where am I going wrong?" As noted, integer division (with truncation) is occurring within the parentheses, before the quotient is cast to float.

“我哪里错了？”正如前面提到的，整数除法(带截断)在圆括号内进行，然后将商强制转换为浮点数。

The simplest solution is to define the variable that will be returned from the float function to be a float itself:

最简单的解决方案是将从Float函数返回的变量定义为Float本身：

float calc_hours( int hours[], int weeks, char output ) {
    float tot = 0.0;

    for( int i = 0; i < weeks; i++ )
        tot += hours[ i ];

    if( output == 'T' )
        return tot; // no casting required

    if( weeks == 0 ) {
        printf( "Division by zero is not defined\n" );
        return -1; // something. Maybe sqrt( -1 );  :-)
    }

    return tot / weeks; // will be 'float' calculation, not integer
}

May as well learn the gotcha now and try to avoid having it bite you later.

不妨现在就了解其中的要害，并尽量避免以后被它咬到。

EDIT

Just thought! A float is limited to ~7 digits of precision, while a 32bit int ranges up to just above 9 digits. If tot is expected to be greater than 999,999, this function may not produce accurate results.

编辑刚想到的！浮点数的精度被限制为~7位，而32位整型的精度最高可达9位以上。如果TOT预期大于999,999，则此函数可能不会产生准确的结果。

As noted in comments, you are casting the result of integer division to float.

正如注释中所指出的，您将整数除法的结果强制转换为浮点数。

(float) (tot / weeks)

You need to cast one of the operands to / to float first to perform floating point math.

要执行浮点运算，您需要先将其中一个操作数强制转换为浮点数。

(float)tot / weeks

• As mentioned by others, code is doing an integer division with an integer quotient. To achieve a floating point quotient, use floating-point math.

  正如其他人所提到的，代码正在用整数商进行整数除法。若要获得浮点商，请使用浮点数学。

  
  



• Also, avoid overflow when adding up the integer values.

  此外，在将整数值相加时避免溢出。

  
  



• Using integer math to perform the summation is good and efficient. Using a float sum readily risks rounding issues if used to sum the ints when hours[] is large.

  使用整数数学来执行求和很好，而且效率很高。如果在小时数[]很大的情况下对整数求和，则使用浮点求和很容易出现舍入问题。

  
  



• In C, consider double for typical floating-point math and save float for select cases where the limited precision and range are specifically needed. Note that printf("%.1f hours\n", calc_hours(hours, weeks, output)); converts the float return value from calc_hours() to double before passing the argument to the printf(...) function.

  在C语言中，对于典型的浮点运算，考虑使用DOUBLE，而对于特别需要有限精度和范围的特定情况，则保存FLOAT。请注意，在将参数传递给printf(...)之前，printf(“%.1f HUTHERS\n”，CALC_HOURS(小时，周，输出))；将浮点返回值从CALC_HOURS()转换为DOUBLE功能。

  
  

// Alternative
double calc_hours(const int hours[], int weeks, char output) {
  long tot = 0; // or long long tot
  for (int i = 0; i < weeks; i++) {
    tot = hours[i] + tot;
  }

  if (output == 'T') {
    return (double) tot;
  }
  return (double) tot / weeks;
}

• Advanced: use size_t for array sizing.

double calc_hours(const int hours[], size_t weeks, char output) {