C - 为什么我的程序没有输出任何东西？

Question

I'm very very new in programming, so i don't know how to solve the problem. As you can see, I want to make a program that outputs location that you want. There is, also, typedef struct for location variables.

    char location[25];
    
    printf("Which place info you want? (Home, School): ");
    scanf("%s", location[25]);
    
    if(!strcmp(location[25], "home"))
    {
        printf("%s\n", home.country);
        printf("%s\n", home.city);
        printf("%s\n", home.street);
        printf("%s\n", home.building_number);
    }
    else if(!strcmp(location[25], "school"))
    {
        printf("%s\n", school.country);
        printf("%s\n", school.city);
        printf("%s\n", school.street);
        printf("%s\n", school.building_number);
    }
    else
    {
        printf("I don't have an info about this place\n");
    }

Answer 1

I think you should rather write ,strcmp(location, "home") , because location[25] is out of bounds and causes an UB (same for the second call to strcmp).

Answer 2

Problem solved by kaylum: scanf("%s", location[25]); -> scanf("%24s", location); and strcmp(location[25], "home") -> strcmp(location, "home")

Answer 3

Inside a declaration, the [25] has a completely different meaning than outside a declaration.

In the line

char location[25];

it means that you are declaring an array of size 25 . However, in the lines

scanf("%s", location[25]);

and

if(!strcmp(location[25], "home"))

the [25] means that you want to access a specific element in the array, in this case the 26 ^th element in the array (arrays indexes start counting at 0, not 1).

Since the array only has 25 characters, attempting to access the 26 ^th element will access the array out of bounds, invoking undefined behavior .

Even if you weren't accessing the array out of bounds, your code would still be wrong. The functions scanf and strcmp both expect a pointer to the first element of the array. Therefore, passing the value of an individual character by writing location[25] or location[0] is wrong. Instead, you should simply write location . That way, the array will decay to a pointer to the first element, ie to &location[0] .