Question

这是我代码的一部分：

    printf("\nEnter amount of adult tickets:");
    scanf("%d", &TktAdult);
    while (TktAdult<0){
        printf("\nPlease enter a positive number!");
        printf("\nEnter amount of adult tickets:");
        scanf("%d", &TktAdult);
    }

现在它只能阻止用户输入负值，但是如何添加它以便它也阻止用户输入char？

Answer 1

...阻止用户输入负值...

是不可能的。用户输入各种乱码。而是读取用户输入的行并解析它的正确性。使用fgets()进行输入，然后使用sscanf()，strtol()等进行解析。

// return -1 on EOF
int GetPositiveNumber(const char *prompt, const char *reprompt) {
  char buf[100];
  fputs(prompt, stdout);
  fflush(stdout);
  while (fgets(buf, sizeof buf, stdin)) [
    int value;
    if (sscanf(buf, "%d", &value) == 1 && value > 0) {
      return value;
    }
    fputs(reprompt, stdout);
    fflush(stdout);
  }
  return -1;
}

// Usage
int TktAdult = GetPositiveNumber(
    "\nEnter amount of adult tickets:" , 
    "\nPlease enter a positive number!");
if (TktAdult < 0) Handle_End_of_File();
else Success(TktAdult);

Answer 2

但是如何添加它以便它也阻止用户输入char？

您无法阻止用户输入字符值。您可以做的是检查是否已成功扫描tktAdult。如果没有，请从stdin中清除所有内容：

 bool valid = false;
 while (true) {
 ...

    if (scanf("%d", &TktAdult) != 1) {
       int c;
       while ((c = getchar()) != EOF && c != '\n');
    } else {
       break;
    }
}

更好的选择是使用fgets()，然后使用sscanf()解析该行。

另见：Why does everyone say not to use scanf? What should I use instead?。

Answer 3

// You can try this,  Filter all except for the digital characters
int TktAdult;
char ch;
char str[10];
int i = 0;
printf("\nEnter amount of adult tickets:");
while ((ch = getchar()) != '\n')
{
    // Filter all except for the digital characters
    if(!isalpha(ch) && isalnum(ch))
        str[i++] = ch;
}
str[i] = '\0';
TktAdult = atoi(str);
printf("Done [%d]\n", TktAdult);

Answer 4

以下代码拒绝以下用户输入：

非数字，由// 1;
由// 2处理的负数;

正数后跟非数字字符，由// 3

处理

while (1) {
    printf("\nEnter amount of adult tickets: ");
    if (scanf("%d", &TktAdult) < 0 ||  // 1
            TktAdult < 0 ||  // 2
            ((next = getchar()) != EOF && next != '\n')) {  // 3
        clearerr(stdin);
        do
            next = getchar();
        while (next != EOF && next != '\n');  // 4
        clearerr(stdin);
        printf("\nPlease enter a positive number!");
    } else {
        break;
    }
}

此外，// 4清除缓冲的非数字字符的标准输入，大小写为// 3（即123sda - scanf需要123但在缓冲区中留下'sda'。）

Answer 5

#include <stdio.h>

int main() {
    int x = 0.0;
    int readReasult;
    while(1)
    {
        readReasult = scanf("%d",&x);
        if (readReasult < 0) break;
        if (readReasult == 1) {
            if (x >= 0)
                printf("next number: %d\n", x);
            else
                printf("negative value not expected\n");
        } else {
            clearerr(stdin);
            scanf("%*s");
            printf("wrong input\n");
        }
    }

    return 0;
}

https://godbolt.org/z/xn86qz

如何阻止用户在C中输入char作为int输入

5 个答案: