将多个if更改为循环？

【问题标题】：Change multiple if to a loop?将多个if更改为循环？
【发布时间】：2015-12-22 12:29:19
【问题描述】：

我刚刚学会了如何使用循环，但我不知道如何翻译这段代码：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    float manyTest, gr1, gr2, gr3, gr4, gr5, gr6, gr7, gr8, gr9, gr10, gr11, gr12, gr13, gr14, gr15, gr16, gr17, gr18, gr19, gr20, gr21, gr22, gr23, gr24, gr25;
    manyTest = gr1 = gr2 = gr3 = gr4 = gr5 = gr6 = gr7 = gr8 = gr9 = gr10 = gr11 = gr12 = gr13 = gr14 = gr15 = gr16 = gr17 = gr18 = gr19 = gr20 = gr21 = gr22 = gr23 = gr24 = gr25 = 0;

    printf("How many tests you wanna average? (Minimum 1 Maximum 25)\n");
    scanf(" %f", &manyTest);
    if (manyTest <= 0) {
        printf("The Minimum is 1!\n");

    }
    else if (manyTest > 25){
        printf("The Maximum is 25!\n");

    }
    else {
        if (manyTest == 1) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
        }
        else if (manyTest == 2) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
        }
        else if (manyTest == 3) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);

        }
        else if (manyTest == 4) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);

        }
        else if (manyTest == 5) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
        }
        else if (manyTest == 6) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);

        }
        else if (manyTest == 7) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
        }
        else if (manyTest == 8) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr2);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
        }
        else if (manyTest == 9) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
        }
        else if (manyTest == 10) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
        }
        else if (manyTest == 11) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
        }
        else if (manyTest == 12) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
        }
        else if (manyTest == 13) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
        }
        else if (manyTest == 14) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
        }
        else if (manyTest == 15) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
        }
        else if (manyTest == 16) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
        }
        else if (manyTest == 17) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
        }
        else if (manyTest == 18) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
        }
        else if (manyTest == 19) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
            scanf(" %f", &gr19);
        }
        else if (manyTest == 20) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
            scanf(" %f", &gr19);
            scanf(" %f", &gr20);
        }
        else if (manyTest == 21) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
            scanf(" %f", &gr19);
            scanf(" %f", &gr20);
            scanf(" %f", &gr21);
        }
        else if (manyTest == 22) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
            scanf(" %f", &gr19);
            scanf(" %f", &gr20);
            scanf(" %f", &gr21);
            scanf(" %f", &gr22);
        }
        else if (manyTest == 23) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
            scanf(" %f", &gr19);
            scanf(" %f", &gr20);
            scanf(" %f", &gr21);
            scanf(" %f", &gr22);
            scanf(" %f", &gr23);
        }
        else if (manyTest == 24) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
            scanf(" %f", &gr19);
            scanf(" %f", &gr20);
            scanf(" %f", &gr21);
            scanf(" %f", &gr22);
            scanf(" %f", &gr23);
            scanf(" %f", &gr24);
        }
        else if (manyTest == 25) {
            printf("Write down your grades on those tests:\n");
            scanf(" %f", &gr1);
            scanf(" %f", &gr2);
            scanf(" %f", &gr3);
            scanf(" %f", &gr4);
            scanf(" %f", &gr5);
            scanf(" %f", &gr6);
            scanf(" %f", &gr7);
            scanf(" %f", &gr8);
            scanf(" %f", &gr9);
            scanf(" %f", &gr10);
            scanf(" %f", &gr11);
            scanf(" %f", &gr12);
            scanf(" %f", &gr13);
            scanf(" %f", &gr14);
            scanf(" %f", &gr15);
            scanf(" %f", &gr16);
            scanf(" %f", &gr17);
            scanf(" %f", &gr18);
            scanf(" %f", &gr19);
            scanf(" %f", &gr20);
            scanf(" %f", &gr21);
            scanf(" %f", &gr22);
            scanf(" %f", &gr23);
            scanf(" %f", &gr24);
            scanf(" %f", &gr25);
        }
        float avg = (gr1 + gr2 + gr3 + gr4 + gr5 + gr6 + gr7 + gr8 + gr9 + gr10 + gr11 + gr12 + gr13 + gr14 + gr15 + gr16 + gr17 + gr18 + gr19 + gr20 + gr21 + gr22 + gr23 + gr24 + gr25) / manyTest;
        printf("Your average grade is: %.2f\n", avg);

    }

    system("pause");
    return 0;

}

从所有这些if...if...if...if....if 到一些单个循环。如您所见，我的代码很长，而且是在我学会如何使用循环之前完成的。所以，现在我学会了我不知道该怎么做。

【问题讨论】：

  • 使用循环和数组。
  • 你需要使用数组而不是你的变量gr1, gr2
  • 你不能循环不同的变量，但是你可以循环一个数组。
  • 如果最大值为 100，你将如何编写该代码？
  • 你用scanf()错了很多次！为什么不使用数组？是禁止的吗？

标签： c loops if-statement


【解决方案1】：

您需要的只是一个循环用于您的manyTest 值，您根本不需要数组！

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    float manyTest = 0, gr = 0, avg = 0; //firstly, replace many gr with single gr, avg for averaging
    int i; //just indexer

    printf("How many tests you wanna average? (Minimum 1 Maximum 25)\n");
    scanf(" %f", &manyTest);
    if (manyTest <= 0) {
        printf("The Minimum is 1!\n");
    }
    else if (manyTest > 25){
        printf("The Maximum is 25!\n");
    }
    else {
        printf("Write down your grades on those tests:\n");
        for (i = 0; i < manyTest; ++i) {
            scanf(" %f", &gr); //use gr every time
            avg += gr; //then immediately add to avg!
        }
        printf("Your average grade is: %.2f\n", avg / manyTest); //notice the division by manyTest
    }

    system("pause");
    return 0;
}

完成！

示例结果：

【讨论】：

    【解决方案2】：

    这是一个相对稳健且完整的示例，它不限制输入的总量。相反，您发送 EOF 来结束输入流：

    #include <errno.h>
#include <stdio.h>

int main() {
  int total = 0;
  double acc = 0, val;

  for (;;) {
    fputs("Value: ", stdout);
    fflush(stdout);

    errno = 0;
    int res = fscanf(stdin, "%lf", &val);

    if (res == EOF) {
      // Handle successful end of input or read error.
      if (errno == 0) {
        fprintf(stdout, "Done! You entered %d values averaging %f.\n",
                total, acc / total);
      } else {
        fputs("There was an error, aborting!\n", stdout);
      }
      break;
    } else if (res == 0) {
      // Handle parse error.
      fputs("Sorry, I did not understand. Try again.\n", stdout);
      clearerr(stdin);
      for (int r = 0; r != EOF && r != '\n'; r = fgetc(stdin)) {}
    } else {
      // Handle successful input.
      acc += val;
      ++total;
    }
  }
}

    Demo

    【讨论】：

    • 我希望有足够的错误来确保复制/粘贴它会得到一个糟糕的成绩:)
    【解决方案3】：

    有一种方法可以计算一组数字的平均值，而无需将每个数字单独存储在数组中或单独命名变量（yuk）中。

    只保留一个累计，最后除以。

    【讨论】：

      【解决方案4】：

      您可以使用数组，然后迭代以获取输入。

      这样的事情是可以做到的——

      int n;                          // number of tests
scanf("%d",&n);                 // take input number of tests 
int grades[n];                  // declare your array 
for(int i=0;i<n;i++){           // loop for n times
   scanf(" %d",&grades[i]);     // take input n number of grades 
}

      【讨论】：

      • 别忘了跳过换行符。
      • 问题不在于减少 if..else 吗？
      • @Bathsheba 我从来没有说过这很糟糕，只是优先级，你知道的。 :)
      • @Bathsheba 先生，我并没有真正理解你的第一条评论。
      • 我认为你在for 循环中需要scanf(" %。注意空格
      【解决方案5】：

      要回答第一部分，关于减少if...else 条件检查，您不能全部从代码中删除if..else 条件，但是，您可以肯定地减少else 部分。为此，您需要使用switch statement。类似的东西

      if (manyTest <= 0) {
    printf("The Minimum is 1!\n");

}
else if (manyTest > 25){
    printf("The Maximum is 25!\n");

}
else {
    switch(manyTest)
    {

       case 1: //.... break;
       case 2: //..... break;
    }

      可以帮到你。

      然后，为了减少代码中使用的变量数量，您可以使用array，并使用for 循环迭代一定次数以填充所需数量的输入。

      【讨论】：

      • 谢谢，但我不知道如何使用 switch 语句。你能解释一下怎么做吗？或者你说我应该继续学习直到我能够使用它？
      • @kuyy 那么是时候学习了。我已经用一个简单教程的链接更新了我的答案。希望对您有所帮助。
      【解决方案6】：

      您可以使用简单的数组作为成绩输入和平均值，这对您来说只是领先一步

      int main()
{
    int manyTest = 0;
    float gr[25];

    printf("How many tests you wanna average? (Minimum 1 Maximum 25)\n");
    scanf(" %f", &manyTest);
    if (manyTest <= 0) {
        printf("The Minimum is 1!\n");

    }
    else if (manyTest > 25){
        printf("The Maximum is 25!\n");

    }
    for(int i=0;i<manyTest;i++){
        printf("Write down your grades for test %d:",i);
         scanf(" %f", &gr[i]);
    }
//Average
    float avg;
    for(int j=0; j<manyTest;j++){
        avg+=gr[j];
    }
    avg=(avg/manyTest);
    printf("Your average grade is: %.2f\n", avg);
}

      【讨论】：

      • 好像不太好用。它只是一直问我“blalahlahl 考试成绩 number”
      • grade for test 在 for 循环中，它的运行时间与 manyTest 的输入完全相同
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