c - 很难在 C 中将结果相加(For 循环)

Question

我用 C 语言编写了这段代码。它的基本功能是接受用户的输入(数字)，并且根据用户选择的数字，它将运行一个 for 循环。 for 循环将要求用户根据其要求的语句输入更多数字。然后，代码将从用户那里获取这些输入并将其应用到公式中。

假设用户首先输入2。它应该做的是循环两次，并从第一次和第二次中取出总和并将它们加在一起。不幸的是，它不会这样做，只会返回循环中的第一个结果，并与第二个结果分开。

这是代码:

#include <stdio.h>
int main(){

    int i = 0;
    int robotMany = 0;
    int enginePower = 0;
    int resistance = 0;
    int weight = 0;
    int height = 0;

    printf("Depending the numbers of robot that you enter.You will need to do the following\n");
    printf("Engine power\nResistance\nWeight\nHeight\n");

    printf("Enter the amount of robots\n");
    scanf("%d",&robotMany);
    printf("You chose %d robot\n", robotMany);

    //Depending  the user input, it will run # of times.
    for(i = 0; i < robotMany; i++){

        //for loop begins
        printf("Enter the engine power.(1-20)\n");
        scanf("%d", &enginePower);
        printf("Enter the resistance.(1-3)\n");
        scanf("%d", &resistance);
        printf("Enter the weight of the robot\n");
        scanf("%d", &weight);
        printf("Enter the height of Robot.\n");
        scanf("%d", &height);
        int product;
        //take the user inputs and apply it to the formual.
        product = (enginePower + resistance) * (weight - height); 

        printf("This is your total power\n");
        printf("%d\n", product);
    }

    return 0;
}

Answer 1

您存在一个基本逻辑错误，即未能保持每次循环迭代中计算的product 的运行总计。

但是，您遇到了一个更大的问题，即无法验证 scanf(或用于用户输入的任何函数)的返回。验证每个用户输入至关重要，在使用 scanf 以避免在代码中调用未定义行为时更是如此。为什么？如果用户输入的杂散字符与格式字符串中的转换说明符不匹配，则会发生匹配失败，并从中提取字符>stdin 此时停止，将有问题的字符留在输入缓冲区中未读。在您的情况下，这将导致在程序的其余部分中每次调用 scanf 时都会出现相同的匹配失败。

例如，用户在输入 robotMany 时按下了 '2' 键，但意外点击了 'w' 键。不仅 robotMany 的输入失败，而且由于 'w' 留在 stdin 中未读，导致enginePower、阻力、重量和高度的输入也失败。 (如果这种情况发生在循环内，您的循环可能会失去控制，直到手动终止该进程)

这就是为什么始终验证任何输入函数的返回至关重要，尤其是 scanf 系列函数。要捕获并处理任何输入失败(匹配失败、输入失败或手动生成的 EOF)，只需检查返回，例如

    if (scanf ("%d", &robotMany) != 1) {    /* VALIDATE EVERY USER INPUT! */
        fputs ("error: invalid input, or user canceled - robotMany\n", stderr);
        return 1;
    }

关于你的逻辑错误。首先，您需要一个变量来跟踪循环每次行程中计算出的每个product 的总和。由于看起来这将是总功率，因此只需添加一个 totalpwr 变量并将其初始化为零(因为您已经很好地处理了所有变量)，例如

    int i = 0,
        robotMany = 0,
        enginePower = 0,
        resistance = 0,
        weight = 0,
        height = 0,
        totalpwr = 0;   /* sum of product from each iteration */

现在，在循环中，您希望每次计算时将 product 添加到 totalpwr 中，例如

    /* Depending  the user input, it will run # of times. */
    for (i = 0; i < robotMany; i++) {
        ...
        /* take the user inputs and apply it to the formula. */
        int product = (enginePower + resistance) * (weight - height);

        totalpwr += product;    /* add product to total power */
    }

要输出totalpwr，您将输出退出循环后的值，例如

         ...
    }

    /* you output the total power required outside the loop */
    printf ("\ntotal power required: %d\n", totalpwr);

    return 0;
}

将其完全放在一个示例中(不传递 product 计算的正确性或所需值的范围)，您可以执行类似于以下操作的操作:

#include <stdio.h>

int main (void) {

    int i = 0,
        robotMany = 0,
        enginePower = 0,
        resistance = 0,
        weight = 0,
        height = 0,
        totalpwr = 0;   /* sum of product from each iteration */

    /* you only need a single printf (fputs would do due to no conversion) */
    printf ("Depending the numbers of robot that you enter, you will need "
            "to enter:\n\n"
            "  Engine power | Resistance | Weight | Height\n\n"
            "Enter the amount of robots: ");
    if (scanf ("%d", &robotMany) != 1) {    /* VALIDATE EVERY USER INPUT! */
        fputs ("error: invalid input, or user canceled - robotMany\n", stderr);
        return 1;
    }

    printf ("\nYou chose: %d robots\n\n", robotMany);

    /* Depending  the user input, it will run # of times. */
    for (i = 0; i < robotMany; i++) {
        printf ("Enter the engine power.(1-20): ");
        if (scanf("%d", &enginePower) != 1) {   /* validate! */
            fputs ("error: invalid input - enginePower\n", stderr);
            return 1;
        }

        printf ("Enter the resistance.(1-3): ");
        if (scanf("%d", &resistance) != 1) {    /* validate! */
            fputs ("error: invalid input - resistance\n", stderr);
            return 1;
        }

        printf ("Enter the weight of the robot: ");
        if (scanf("%d", &weight) != 1) {        /* validate! */
            fputs ("error: invalid input - weight\n", stderr);
            return 1;
        }

        printf ("Enter the height of Robot: ");
        if (scanf("%d", &height) != 1) {        /* validate! */
            fputs ("error: invalid input - height\n", stderr);
            return 1;
        }

        /* take the user inputs and apply it to the formula. */
        int product = (enginePower + resistance) * (weight - height);
        /* the following outputs the per-loop/per-robot product (you can remove) */
        printf ("  iteration %d product: %d\n\n", i+1, product);

        totalpwr += product;    /* add product to total power */
    }

    /* you output the total power required outside the loop */
    printf ("\ntotal power required: %d\n", totalpwr);

    return 0;
}

(注意:只需一个printf即可输出多行输出，无需逐行重复调用。所有顺序字符串将由编译器连接)

示例使用/输出

$ ./bin/robotmany
Depending the numbers of robot that you enter, you will need to enter:

  Engine power | Resistance | Weight | Height

Enter the amount of robots: 3

You chose: 3 robots

Enter the engine power.(1-20): 4
Enter the resistance.(1-3): 2
Enter the weight of the robot: 10
Enter the height of Robot: 31
  iteration 1 product: -126

Enter the engine power.(1-20): 5
Enter the resistance.(1-3): 3
Enter the weight of the robot: 9
Enter the height of Robot: 31
  iteration 2 product: -176

Enter the engine power.(1-20): 3
Enter the resistance.(1-3): 1
Enter the weight of the robot: 8
Enter the height of Robot: 31
  iteration 3 product: -92

total power required: -394

您可能希望在重量和高度条目上添加约束，以防止出现负的所需功率结果 - 但这由您决定。检查一下，如果您还有其他问题，请告诉我。