有沒有辦法在forloop結束后顯示“未找到數字”？

#include <stdio.h>
void main()
{
    int n,i;
    int arr[5]={5,4,3,2,1};
    int *ptr;
    printf("input the number you want to find:\n");
    scanf("%d",&n);
    for(i=0;i<5;i  )
        if(arr[i]==n)
        {
            ptr=&arr[i];
        printf("number '%d' is present in the array and it is the %d st/nd/rd/th term in the array.\n its address is: %d",n,i 1,ptr);
        }
}

**> 我添加了 else printf("number not found"); 在這里，但它也回圈和列印了很多 **

uj5u.com熱心網友回復：

保持簡單......只需在回圈后添加列印并在匹配時添加回傳。

喜歡：

#include <stdio.h>
int main(void)
{
    int n,i;
    int arr[5]={5,4,3,2,1};
    int *ptr;
    printf("input the number you want to find:\n");
    if (scanf("%d",&n) != 1)
    {
        // Input error
        exit(1);
    }
    for(i=0;i<5;i  )
    {
        if(arr[i]==n)
        {
            ptr=&arr[i];
            printf("number '%d' is present in the array and it is the %d st/nd/rd/th term in the array.\n its address is: %p",n,i 1,(void*)ptr);
            return 0;  // Done... just end the program
        }
    }
    puts("not found");
}

順便提一句：

注意它應該是 int main(void)

注意，指標是使用被列印%p有澆注到(void*)

uj5u.com熱心網友回復：

1. 始終檢查scanf!!的回傳值
2. 初始化指向 NULL 的指標。如果什么也沒找到，它將保持為 NULL
3. 使用正確的地址格式 ( %p)，并(void *)在傳遞給之前將指標轉換為printf
4. main回傳型別是int.

int main()
{
    int n;
    int arr[]={5,4,3,5,2,5,1};
    int *ptr = NULL;
    printf("input the number you want to find:\n");
    if(scanf("%d",&n) == 1)
    {
        for(size_t i=0;i<sizeof(arr)/ sizeof(arr[0]);i  )
            if(arr[i]==n)
            {
                ptr=&arr[i];
                printf("number '%d' is present in the array and it is the %zu st/nd/rd/th term in the array.\n its address is: %p",n,i 1, (void *)ptr);
            }
        if(!ptr) printf("NUMBER NOT FOUND!!!!!\n");
    }
    else
    {
        printf("SCANF ERROR\n");
    }
}

https://godbolt.org/z/6zcE4nnz8

uj5u.com熱心網友回復：

只需將 printf 的呼叫放在 for 回圈之外。例如

int *ptr = NULL;

printf("input the number you want to find:\n");
scanf("%d",&n);

for( i = 0; ptr == NULL && i < 5; i   )
{
    if ( arr[i] == n )
    {
        ptr = arr   i;
    }
}

if ( ptr != NULL )
{
    printf("number '%d' is present in the array and it is the %td st/nd/rd/th term in the array.\n its address is: %p\n", 
           n, ptr - arr   1, ( void * )ptr );
}
else
{
    printf( "number %d is not present in the array.\n", n );
}

也不要使用像5. 而是使用命名常量。并在使用它們的最小范圍內宣告變數。并且使用%d帶有指標的轉換說明符具有未定義的行為。您需要使用轉換說明符%p。

這是一個演示程式。

#include <stdio.h>

int main(void) 
{
    int arr[] = { 5, 4, 3, 2, 1 };
    const size_t N = sizeof( arr ) / sizeof( *arr );
    
    int n = 0;
    
    printf( "input the number you want to find (default is %d): ", n );
    scanf( "%d", &n );
    
    int *ptr = NULL;
    
    for ( size_t i = 0; ptr == NULL && i < N; i   )
    {
        if ( arr[i] == n )
        {
            ptr = arr   i;
        }
    }

    if ( ptr != NULL )
    {
        printf( "number '%d' is present in the array and it is the %td st/nd/rd/th term in the array.\n its address is: %p\n", 
                n, ptr - arr   1, ( void * )ptr);
    }
    else
    {
        printf( "number %d is not present in the array.\n", n );
    }
}

程式輸出可能看起來像

input the number you want to find (default is 0): 3
number '3' is present in the array and it is the 3 st/nd/rd/th term in the array.
 its address is: 0x7ffefecb1778

標籤：数组 C 功能 for循环 if 语句

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