Question

我是愿意学习c的学生。我的问题是，用户需要输入形状名称，并且该形状名称应通过switch语句。但是我做不到。因为我不知道如何将字符串传递给switch语句。那有人可以帮我吗？我将添加代码以供参考。

#include <stdio.h>

int main(){
int h,w,r,l,area;
char shape[8];

printf("Please select a shape = ");
scanf("%s",&shape);

switch(shape[8]){
case 'circle':
    printf("Enter value for radius = ");
    scanf("%d",&r);

    area = 3.14*r*r;

    printf("Area of circle is = %d",area);
    break;
case 'square':
    printf("Enter value for width = ");
    scanf("%d",&w);

    area = w*w;

    printf("Area of square is = %d",area);
    break;
case 'rectangle':
    printf("Enter value for width = ");
    scanf("%d",&w);
    printf("Enter value for height = ");
    scanf("%d",&h);

    area = w*h;

    printf("Area of rectangle is %d",area);
    break;
case 'triangle':
    printf("Enter value for length = ");
    scanf("%d",&l);
    printf("Enter value for height = ");
    scanf("%d",&h);

    area = 1/2*l*w;

    printf("Area of triangle is = %d",area);
    break;
default:
    printf("Invalid Shape");

}
return 0;

}

Answer 1

不推荐使用switch()来处理此问题，但是您可以做到。您将创建一个查找表（有效形状的字符串文字数组），并在检查用户输入是否为有效形状时，将保存与有效形状相对应的索引，并将该索引传递为{ {1}}变量。然后，您的案例将是整数值，您可以采取适当的措施。

例如，您可以使用以下命令创建一个简单的查找表：

switch()

/* lookup-table (array of pointers to string-literals) */ const char *shapes[] = { "circle", "square", "rectangle", "triangle" }; /* if you need a constant, #define one (or more) */ #define NSHAPES (int)(sizeof shapes / sizeof *shapes)是NSHAPES数组中形状的数量（您可以只使用shapes，但要避免对数字进行硬编码... MagicNumbers 。）

然后，您可以创建一个简单的函数来遍历数组，将用户输入的形状与查找表中的每个形状进行比较，如果找到则返回索引，如果找不到则返回4，例如

-1

然后在/* function to validate shape is one of the valid shapes */ int validshape (const char *shape) { for (int i = 0; i < NSHAPES; i++) /* loop over each shape */ if (strcmp (shape, shapes[i]) == 0) /* compare shape with shapes[i] */ return i; /* return index if found */ return -1; /* return -1 if no match found */ }中，接受用户输入，然后简单地将字符串传递给函数并进行验证，例如

main()

使用int shape = -1; ... shape = validshape (line); /* get shape index (-1 if none) */ if (shape != -1) /* check index is valid */ break; /* (break loop if valid) */ /* otherwise handle error, show allowed */ fputs (" error : invalid input.\n", stderr);中的有效索引，您可以然后shape，例如

switch(shape)

您可以更新每种情况以处理您的算术。

完整版本（使用fputs ("\nvalid : ", stdout); switch (shape) { case 0: puts (shapes[0]); break; case 1: puts (shapes[1]); break; case 2: puts (shapes[2]); break; case 3: puts (shapes[3]); break; default: fputs ("oops -- shouldn't get here\n", stderr); }进行用户输入，因此新的C程序员不会陷入与fgets()进行用户输入相关的许多陷阱中，可以这样做：

scanf()

使用/输出示例

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

/* lookup-table (array of pointers to string-literals) */
const char *shapes[] = { "circle", "square", "rectangle", "triangle" };

/* if you need a constant, #define one (or more) */
#define NSHAPES (int)(sizeof shapes / sizeof *shapes)
#define MAXC 1024

/* simple function to show allowed shapes */
void showallowed (void)
{
    fputs ("  allowed :", stdout);              /* output prefix */
    for (int i = 0; i < NSHAPES; i++)           /* loop over each shape */
        printf (" %s", shapes[i]);              /* output shape */
    putchar ('\n');                             /* tidy up with newline */
}

/* function to validate shape is one of the valid shapes */
int validshape (const char *shape)
{
    for (int i = 0; i < NSHAPES; i++)           /* loop over each shape */
        if (strcmp (shape, shapes[i]) == 0)     /* compare shape with shapes[i] */
            return i;                           /* return index if found */
    
    return -1;                                  /* return -1 if no match found */
}

int main (void) {
    
    char line[MAXC];                            /* buffer to hold all user-input */
    int shape = -1;
    
    while (1) { /* loop continually */
        fputs ("\nenter shape: ", stdout);      /* output prompt for shape */
        if (!fgets (line, MAXC, stdin))         /* validate user input */
            return 1;
        line[strcspn (line, "\n")] = 0;         /* trim \n from end of line */
        shape = validshape (line);              /* get shape index (-1 if none) */
        if (shape != -1)                        /* check index is valid  */
            break;                              /* (break loop if valid) */
        /* otherwise handle error, show allowed */
        fputs ("  error   : invalid input.\n", stderr);
        showallowed();
    }
    
    fputs ("\nvalid : ", stdout);
    switch (shape) {
        case 0: puts (shapes[0]); break;
        case 1: puts (shapes[1]); break;
        case 2: puts (shapes[2]); break;
        case 3: puts (shapes[3]); break;
        default: fputs ("oops -- shouldn't get here\n", stderr);
    }
}

如果您还有其他问题，请告诉我。

Answer 2

不幸的是，C不支持在case语句中传递字符串，因此要避免这种情况，您可以将if-else与strcmp()一起使用，或者为每个形状分配一个数字，然后将其传递给switch语句。

在switch语句之前输入字符串，并使用switch语句比较c中的字符串

2 个答案: