c - 初学者 C - 尝试在数组填满时终止循环

Question

我有一个家庭作业问题，我必须记录成绩，将它们放入数组中，并给出平均值。该程序应该要求输入，直到给出负数作为成绩或数组被填充为止。到目前为止，我能够使程序循环，直到我给出负数，并且它计算出正确的平均值。我不明白的是当数组被填满时如何终止循环。我的代码:

#include <stdio.h>

/* function main begins program execution */
int main( void )
{  int counter; /* number of grade to be entered next */
   int grade; /* grade value */
   int total; /* sum of grades input by user */
   double average; /* average of grades */

   /* initialization phase */
   total = 0; /* initialize total */
   counter = 0; /* initialize counter */
   grade = 0;  /* initialize grade */

   printf( "Input a negative number when done entering grades.\n" );

   /* processing phase */
   #define MAX_GRADES 20
   int grades [MAX_GRADES];
   while ( counter < MAX_GRADES) {
     while ( grade >= 0 ) { /* loop until negative given */
       printf( "Enter grade: " ); /* prompt for input */
       scanf( "%d", &grade ); /* read grade from user */
       if (grade >= 0) {
     if (grade > 100)
       printf( "Grade is greater than 100. Please input grade again.\n" );
     else {
       grades[counter] = grade;
       total = total + grade; /* add grade to total */
       counter = counter + 1;
     } /* end else */
       } /* end if */
     } /* end while */
   } /* end while */

   /* termination phase */
    average = total /(double) counter; /* integer division */

   printf( "Class average is %f\n", average ); /* display result */
   return 0; /* indicate program ended successfully */
} /* end function main */

Answer 1

while ( counter < MAX_GRADES) {
    while ( grade >= 0 ) {

循环中的循环将迭代 x*y 次。外层循环的每一步，内层循环都会从头到尾运行。

您需要一个循环来检查这两个条件:

while ( counter < MAX_GRADES && grade >= 0) 

但是，因为您想首先执行操作，然后检查条件，所以 do..while 循环更适合这里。您还可以随时中断跳出一个循环，或继续完成当前运行并移至下一个:

do{ /* loop */
   printf( "Enter grade: " ); /* prompt for input */
   scanf( "%d", &grade ); /* read grade from user */
   if (grade < 0)
     break;

   if (grade > 100){
     printf( "Grade is greater than 100. Please input grade again.\n" );
     continue;  
   }

   /* all abnormal conditions have been handled */
   /* now we're clear to do the actual job */

   grades[counter] = grade;
   total = total + grade; /* add grade to total */
   counter = counter + 1;

 }while ( counter < MAX_GRADES ) /*until array is full*/