c - printf 在 while 循环中发生两次？

Question

这个问题已经有答案了:

Scanf skips every other while loop in C (10 个回答)

已关闭 5 年前。

所以我是编程的初学者，我想尝试制作一个基本的计算器，给出两个数字的总和或乘积。然而，在 while该程序的循环，第一个 printf似乎在循环的第一次迭代后打印两次。任何纠正此问题的帮助将不胜感激。

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

int multiply(int a, int b) {
    return a * b;
}

void printMultiply(int x, int y) {
    int result = multiply(x, y);
    printf("\n%d\n", result);
}

int add(int a, int b) {
    return a + b;
}

void printAdd(int x, int y) {
    int result = add(x, y);
    printf("\n%d\n", result);
}

int main() {
    int product1 = 0;
    int product2 = 0;

    int sum1 = 0;
    int sum2 = 0;

    while (true) {
        // this prints twice after first iteration?
        printf("Would you like to add or multiply? (press a or  m)\n");

        char choice = ' ';
        scanf("%c", &choice);

        if (choice == 'm') {
            printf("What two numbers would you like to multiply? (leave a space between numbers\n");
            scanf("%d%d", &product1, &product2);
            printMultiply(product1, product2);
        } else
        if (choice == 'a') {
            printf("What two numbers would you like to add?  (leave a space between numbers\n");

            scanf("%d%d", &sum1, &sum2);
            printAdd(sum1, sum2);
        }
    }
}

Answer 1

第一次迭代后，您会在第一次调用 scanf 时看到换行符 (\n)。

您需要做的就是在格式字符串中使用前导空格来消除所有空格:

scanf(" %c", &choice);