為什么這個用于與用戶輸入進行字串比較的代碼不編譯？

#include <stdio.h>
int main()
{
    int age;
    char marietal_status[15], sex[15];

    printf("Age, Marietal status, sex of the driver : ");
    scanf("%i %s %s", &age, marietal_status, sex);

    if((marietal_status == married) || (marietal_status == unmarried && age > 30 && sex == male) 
 || (marietal_status == unmarried && age >25 && sex == female))
    printf("insured");
    else
    printf("uninsured");
}

輸出：

gcc /tmp/NaKWq16d9Q.c -lm
/tmp/NaKWq16d9Q.c: In function 'main':
/tmp/NaKWq16d9Q.c:10:28: error: 'married' undeclared (first use in this function)
   10 |     if((marietal_status == married) || (marietal_status == unmarried && age > 30 && sex == male) || (marietal_status == unmarried && age >25 && sex == female))
      |                            ^~~~~~~
/tmp/NaKWq16d9Q.c:10:28: note: each undeclared identifier is reported only once for each function it appears in
/tmp/NaKWq16d9Q.c:10:60: error: 'unmarried' undeclared (first use in this function)
   10 |     if((marietal_status == married) || (marietal_status == unmarried && age > 30 && sex == male) || (marietal_status == unmarried && age >25 && sex == female))
      |                                                            ^~~~~~~~~
/tmp/NaKWq16d9Q.c:10:92: error: 'male' undeclared (first use in this function)
   10 | ried) || (marietal_status == unmarried && age > 30 && sex == male) || (marietal_status == unmarried && age >25 && sex == female))
      |                                                              ^~~~

/tmp/NaKWq16d9Q.c:10:152: error: 'female' undeclared (first use in this function)
   10 |  && sex == male) || (marietal_status == unmarried && age >25 && sex == female))
      |                                                                        ^~~~~~

uj5u.com熱心網友回復：

married, unmarried,male和female是未宣告的物體。

看來您的意思是字串文字"married","unmarried"和."male""female"

但是像這樣的比較

marietal_status == "married"

將始終評估為 false，因為比較了兩個指標。

相反，您需要使用strcmp在 header 中宣告的 C 字串函式<string.h>。

所以 if 陳述句看起來

#include <string.h>

//...

if( ( strcmp( marietal_status, "married" ) == 0) || 
    ( strcmp( marietal_status, "unmarried" ) == 0 && 
      age > 30 && strcmp( sex, "male" ) == 0 ) 
    || ( strcmp( marietal_status, "unmarried" ) == 0 && age >25 && strcmp( sex, "female" ) == 0 ) )

uj5u.com熱心網友回復：

在C你不能比較兩個char arrayusing ==。您必須使用strcmp如下功能：

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

int main()
{
    int age;
    char marietal_status[15], sex[15];

    printf("Age, Marietal status, sex of the driver : ");
    scanf("%i %s %s", &age, marietal_status, sex);

    if(strcmp(marietal_status, "married") == 0 || (strcmp(marietal_status, "unmarried") == 0 && age > 30 && strcmp(sex, "male")) 
 || (strcmp(marietal_status, "unmarried") == 0 && age >25 && strcmp(sex, "female") == 0))
        printf("insured");
    else
        printf("uninsured");
}

uj5u.com熱心網友回復：

你試圖比較一個變數，編譯器告訴你它是未宣告的（這意味著它不存在，你沒有像 int age 那樣設定它，例如它是一個宣告的變數）。

處理字串時使用雙引號，"

例如初始化字串時，char sex[15] = "female";

所以你的 if 條件應該是這樣的：

if((strcmp(marietal_status, "married") == 0) || (strcmp(marietal_status, "unmarried") == 0) && age > 30 && (strcmp(sex, "male") == 0) || (strcmp(marietal_status, "unmarried") == 0) && age >25 && (strcmp(sex,  "female") == 0))

運行它會產生這個：

./a.out
Age, Marietal status, sex of the driver : 23 unmarried male
uninsured

請注意，這意味著您希望用戶準確輸入此內容，否則比較將無法匹配。我建議閱讀 C 教程，https://www.tutorialspoint.com/cprogramming/index.htm

編輯：正如其他人已經指出的那樣，C 中的字串比較是由 strcmp 函式完成的，不要忘記 #include <string.h>

marietal_status == "unmarried" 可以在 Python 或 JavaScript 等其他語言中使用

標籤：C if 语句 比较 c字符串 字符串文字

上一篇：在Powershell的函式中運行IF陳述句

下一篇：Python中基于同一所有者填充Null地址