如何修复“return 0 / exit(0) 在 for 循环中无法正常工作”？答案

【问题标题】：How to fix "return 0 / exit(0) not working properly inside for loop"?如何修复“return 0 / exit(0) 在 for 循环中无法正常工作”？
【发布时间】：2019-09-17 10:29:28
【问题描述】：

我正在制作一个科学计算器。并考虑循环语句，直到用户通过使用 0 作为选项之一要求停止。但即使在输入 0 之后。它最后一次询问这个语句： printf("Enter two numbers (For only one no. required you can just enter other number anything)\n");

我尝试过使用goto, exit(0) 和return 0 语句。甚至while(1) 和for(;;) 也会循环。

#include <stdio.h>
#include<math.h>
int main()
{
    int a;
    float b,c;
    float d=3.14159/180;
    while(1)
    {
    printf("\nScientific Calculator :\n");
    printf("Enter option:\n 0- Exit, 1-Add, 2-Sub, 3-Multiply, 4-Divide,\n 5-sin(x), 6-cos(x), 7-tan(x), 8-sinh(x), 9-cosh(x), 10-tanh(x),\n11-log10(x),12-exponent,13-power of x w.r.t y \n");
    scanf("%d",&a);
    printf("Enter two numbers (For only one no. required you can just enter other number anything)\n"); //Here is where it starts even after return 0
    scanf("%f%f",&b,&c); //Here after inputting value it ends.
    switch(a)
    {
        case 0:return 0; //Here is the return 0;
        case 1:printf("%d",(int)(b+c)); break;
        case 2:printf("%d",(int)(b-c)); break;
        case 3:printf("%d",(int)(b*c)); break;
        case 4:printf("%f",b/c); break;
        case 5:printf("%f",sin(b*d)); break;
        case 6:printf("%f",cos(b*d)); break;
        case 7:printf("%f",tan(b*d)); break;
        case 8:printf("%f",sinh(b*d)); break;
        case 9:printf("%f",cosh(b*d)); break;
        case 10:printf("%f",cosh(b*d)); break;
        case 11:printf("%f",tanh(b*d)); break;
        case 12:printf("%f",log10(b)); break;
        case 13:printf("%f",exp(b)); break;
        case 14:printf("%f",pow(b,c)); break;
        default:printf("Enter correct option\n");
    }
    }
    return 0;

}

我希望它退出并退出程序，但它要求输入 printf("Enter two numbers ---\n"); 并在输入值后退出。

【问题讨论】：

对scanf进行一些基本检查会很好
你检查case 0太晚了，看我的回答
恕我直言，这更像是printf("Enter two number，它做得太早了，在询问参数之前你应该知道你要对它们做什么。
@OznOg 你是正确的案例 12 和 13
如果选择无效，读数字也没用，我编辑了我的答案

标签： c for-loop while-loop return exit

【解决方案1】：

但即使输入0。它最后一次询问这个语句：printf("Enter two numbers (For only one no. required you can just enter other number anything)\n");

你需要立即检查大小写'0'，所以

 printf("Enter option:\n 0- Exit, 1-Add, 2-Sub, 3-Multiply, 4-Divide,\n 5-sin(x), 6-cos(x), 7-tan(x), 8-sinh(x), 9-cosh(x), 10-tanh(x),\n11-log10(x),12-exponent,13-power of x w.r.t y \n");
 scanf("%d",&a);
 printf("Enter two numbers (For only one no. required you can just enter other number anything)\n"); //Here is where it starts even after return 0
 scanf("%f%f",&b,&c); //Here after inputting value it ends.
 switch(a)
    case 0:return 0; //Here is the return 0;
    case 1:printf("%d",(int)(b+c)); break;
    ...

必须

printf("Enter option:\n 0- Exit, 1-Add, 2-Sub, 3-Multiply, 4-Divide,\n 5-sin(x), 6-cos(x), 7-tan(x), 8-sinh(x), 9-cosh(x), 10-tanh(x),\n11-log10(x),12-exponent,13-power of x w.r.t y \n");
scanf("%d",&a);
if (a == 0)
  return 0;

printf("Enter two numbers (For only one no. required you can just enter other number anything)\n"); //Here is where it starts even after return 0
scanf("%f%f",&b,&c); //Here after inputting value it ends.
switch(a)
   case 1:printf("%d",(int)(b+c)); break;
   ...

请注意，检查是否输入了有效的 int 也是一个好主意，因此要检查 scanf("%d",&a) 是否返回 1，scanf("%f%f",&b,&c) 是否返回 2 也是如此。 .

正如@OznOg 在针对案例 12 和 13 的评论中所说，您只需要读取一个数字，而不是两个。另请注意，如果代码无效，则询问号码是没有用的，所以：

  if (scanf("%d",&a) != 1)
    return -1;

  if (a == 0)
    return 0;

  if ((a < 0) || (a > 14))
    printf("Enter correct option\n");
  else if ((a == 12) || (a == 13)) {
    printf("Enter one number\n");
    if (scanf("%f",&b) != 1)
      return -1;
    if (a == 12)
      printf("%f",log10(b)); 
    else
      printf("%f",exp(b)); break;
  }
  else {
    printf("Enter two numbers\n");
    if (scanf("%f%f",&b,&c) != 2)
      return -1;
    switch(a)
    {
    case 1:printf("%d",(int)(b+c)); break;
    case 2:printf("%d",(int)(b-c)); break;
    case 3:printf("%d",(int)(b*c)); break;
    case 4:printf("%f",b/c); break;
    case 5:printf("%f",sin(b*d)); break;
    case 6:printf("%f",cos(b*d)); break;
    case 7:printf("%f",tan(b*d)); break;
    case 8:printf("%f",sinh(b*d)); break;
    case 9:printf("%f",cosh(b*d)); break;
    case 10:printf("%f",cosh(b*d)); break;
    case 11:printf("%f",tanh(b*d)); break;
    case 14:printf("%f",pow(b,c)); break;
    }
  }

【讨论】：