简单的单位转换程序 - 使用do-while循环扫描scanf（C编程）

我目前遇到的问题是程序没有完成第一个scanf命令之前的部分，只是跳过整个决策过程并返回到do-while循环的开头 . 我已经阅读了其他建议告诉人们使用fgetc（），因为输入转换类型后输入按钮（1-5）在输入缓冲区中创建一个空白区域，这样可以防止这种情况，但我真的不愿意，因为它是不是我目前学习材料的一部分，作为最后的手段，我将使用它，甚至我不知道如何实现代替scanf . 该程序看起来好像已经完成，并将其转换为c代码（我熟悉）允许它工作，但由于某种原因它在C代码中没有与我合作 . 我还尝试了stackoverflow的另一个建议，其中提到使用scanf：scanf（“％c * c”，＆conversionDirection）;这实际上允许它进入下一部分，但有时迫使你输入你的决定两次，第一个输入没有给你一个反应...我真的很感激，如果有人可以从这里测试这个代码的原因我不知道该怎么办，我已经尝试了一切 .

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

int main()
{
    int userChoice;
    char conversionDirection;
    float calculateNumber;

    do
    {
        printf("Please enter one of the following: \n");
        printf("Number\tConversion\n\n");
        printf("1\t Kilogram/Pound\n");
        printf("2\t Litre/Gallon\n");
        printf("3\t Centimeter/Inch\n");
        printf("4\t Celsius/Fahrenheit\n");
        printf("5\t Quit\n");
        scanf("%d", &userChoice);

        if (userChoice == 1)
        {
            printf("Enter 'K' for Kilogram -> Pound or Enter 'P' for Pound -> Kilogram\n");
            scanf("%c", &conversionDirection);

            if (conversionDirection == 'K')
            {
                printf("Please enter the amount of Kilograms\n");
                scanf("%f", &calculateNumber);

                printf("%f Kilograms is equal to %f Pounds\n\n", calculateNumber, calculateNumber * 2.2);
            }
            else if (conversionDirection == 'P')
            {
                printf("Please enter the amount of Pounds\n");
                scanf("%f", &calculateNumber);

                printf("%f Pounds is equal to %f Kilograms\n\n", calculateNumber, calculateNumber / 2.2);
            }
        }
        else if (userChoice == 2)
        {
            printf("Enter 'L' for Litre -> Gallon or Enter 'G' for Gallon -> Litre\n");
            scanf("%c", &conversionDirection);

            if (conversionDirection == 'L')
            {
                printf("Please enter the amount of Litres\n");
                scanf("%f", &calculateNumber);

                printf("%f Liters is equal to %f Gallons\n\n", calculateNumber, calculateNumber * 0.264172);
            }
            else if (conversionDirection == 'G')
            {
                printf("Please enter the amount of Gallons\n");
                scanf("%f", &calculateNumber);

                printf("%f Gallons is equal to %f Liters\n\n", calculateNumber, calculateNumber / 0.264172);
            }
        }
        else if (userChoice == 3)
        {
            printf("Enter 'C' for Centimeter -> Inch or Enter 'I' for Inch -> Centimeter");
            scanf("%c", &conversionDirection);

            if (conversionDirection == 'C')
            {
                printf("Please enter the amount of Centimeters\n");
                scanf("%f", &calculateNumber);

                printf("%f Centimeters is equal to %f Inches\n\n", calculateNumber, calculateNumber * 0.393701);
            }
            else if (conversionDirection == 'I')
            {
                printf("Please enter the amount of Inches\n");
                scanf("%f", &calculateNumber);

                printf("%f Inches is equal to %f Centimeters\n\n", calculateNumber, calculateNumber / 0.393701);
            }
        }
        else if (userChoice == 4)
        {
            printf("Enter 'C' for Celsius -> Fahrenheit or Enter 'F' for Fahrenheit -> Celsius");
            scanf("%c", &conversionDirection);

            if (conversionDirection == 'C')
            {
                printf("How many degrees Celsius?\n");
                scanf("%f", &calculateNumber);

                printf("%f degrees Celsius is equal to %f degrees Fahrenheit\n\n", calculateNumber, (calculateNumber * 9 / 5) + 32);
            }
            else if (conversionDirection == 'F')
            {
                printf("How many degrees Fahrenheit?\n");
                scanf("%f", &calculateNumber);

                printf("%f degrees Fahrenheit is equal to %f degrees Celsius\n\n", calculateNumber, (calculateNumber - 32) * 5 / 9);
            }
        }
        else if (userChoice == 5)
        {
            printf("Program Exit");
            return 0;
        }
        else
        {
            printf("Please enter a valid number");
        }
    } while (userChoice != 5);


    return 0;
}