当我输入值退出程序时打印不工作

Question

我还是 C 编程的新手，需要弄清楚为什么当我输入“c”选项时，程序没有打印出程序中输入的成绩。我没有看到我缺少的东西，如果有人看到我缺少的东西，可以告诉我吗？

#include <stdio.h>
#include <stdlib.h>


int main()
{
    //Add all of the variables and the array for the grades I want to enter.
    char choice;
    int gradeScore = 0;//percentage
    //int gradeArray[100];//percentArrray //Comment Out
    int gCount = 0,i;//count

    //Allocate dynamic memory point using gradeArray.
    int *gradeArray = (int*)malloc(sizeof(int));

    /*The for loop is set to enable the user to enter no more than 100 grades.  This is because the gradeArray variable
    limit is set to 100.  This will then loop through until the user has entered up to 100 grades to ensure there
    is no buffering issue.*/

    for (gCount = 0; gCount < 100;)

        {
        /*This prompts the user for a choice that enables them to either enter another grade or exit the program and
        print the grades.  It also reads the choice entered by the user.*/
        printf("******************Enter Choice Selection in Parenthesis******************");
        printf("\n\n To add grades, enter choice (a)");
        printf("\n When finished entering grades, enter choice (c) \n \nEnter Choice: ");
        scanf(" %c", &choice);  //space is entered to ensure the compiler does not read whitespaces

        /* Then I use an if with the condition set to a valid choice of 'a'.  Then I prompt the user
        to enter a grade, read it and move on to the next if statement.*/
        if(choice == 'a')
        {
            printf("\nEnter grade: ");
            scanf(" %d", &gradeScore);

            /*If the grade entered does meet the if condition statement below it is added to the gCount
            of grades entered. This will allow all of the grades entered to be printed with the exit condition.*/
            if(gradeScore <= 100 && gradeScore >= 0)
            {
                gradeArray = realloc(gradeArray, sizeof(int) * gCount);
            }

        }


        //The last if statement prints out each grade on a new line when the user choice is c.
        if(choice == 'c')
        {
            break;
        }
    }
    printf("Grades are:\n");
    for(i = 0; i < gCount ; i++)
    {
        printf("  %d\%%\n", gradeArray[i]);

    }
    free(gradeArray);
    return 0;
}

谢谢你， 安妮特

Answer 1

根据您的程序，您在 for 循环中使用了错误的变量。您在 for 循环中将 gCount 重新初始化为 0 而不是递增它。稍后您将使用相同的 gCount 打印成绩。但由于它的值为 0，所以没有打印成绩。

Answer 2

问题是你从未增加gCount 变量的值，for() 循环也是错误的，我建议在这里使用while()，你也从未将gradeScore 添加到gradeArray。你可以这样写：

#include <stdio.h>
#include <stdlib.h>

int main()
{
    //Add all of the variables and the array for the grades I want to enter.
    char choice;
    int gradeScore = 0;//percentage
    //int gradeArray[100];//percentArrray //Comment Out
    int gCount = 0,i;//count
 
    //Allocate dynamic memory point using gradeArray.
    int arr_size = 20;
    int *gradeArray = malloc(sizeof(int)*arr_size);

    /*The for loop is set to enable the user to enter no more than 100 grades.  This is because the gradeArray variable
    limit is set to 100.  This will then loop through until the user has entered up to 100 grades to ensure there
    is no buffering issue.*/
    
    while(gCount < 100)
    {
        /*This prompts the user for a choice that enables them to either enter another grade or exit the program and
        print the grades.  It also reads the choice entered by the user.*/
        printf("******************Enter Choice Selection in Parenthesis******************");
        printf("\n\n To add grades, enter choice (a)");
        printf("\n When finished entering grades, enter choice (c) \n \nEnter Choice: ");
        scanf(" %c", &choice);  //space is entered to ensure the compiler does not read whitespaces

        /* Then I use an if with the condition set to a valid choice of 'a'.  Then I prompt the user
        to enter a grade, read it and move on to the next if statement.*/
        if(choice == 'a')
        {
            printf("\nEnter grade: ");
            scanf(" %d", &gradeArray[gCount]);
            
            /*If the grade entered does meet the if condition statement below it is added to the gCount
            of grades entered. This will allow all of the grades entered to be printed with the exit condition.*/
            if((gCount+1) == arr_size)
            {
                arr_size += 20;
                gradeArray = realloc(gradeArray, sizeof(int) * arr_size);
            }
            
            gCount++;
        }


        //The last if statement prints out each grade on a new line when the user choice is c.
        if(choice == 'c')
        {
            break;
        }
    }
    
    printf("Grades are:\n");
    for(i = 0; i < gCount ; i++)
    {
        printf("  %d\%%\n", gradeArray[i]);

    }
    
    free(gradeArray);
    return 0;
}

另外，我想指出的是，您不应该只分配一个元素的数组并不断地重新分配它。这是一种不好的做法，既费时又会在以后导致一些更大的问题。

我建议您检查此Do I cast the result of malloc? 进行 malloc 转换。