指向 C 中数组的第一个元素

Question

I'm sorry if this questions has already been asked, I searched a bit before posting, but couldn't find an answer to it.

I have this code:

#include<stdio.h>
#include<stdlib.h>

#define ESC 27

typedef struct{
    int data[10];
    int n;
} tlist;

void menu(){
    printf("Options:\n");
    printf("1) Show list\n");
    printf("ESC) Quit\n");
}

void showList(tlist *list){
    int *p;
    p = &list->data[0];
    if(list->n == 0){
        printf("Empty list!\n\n");
    }else{
        for(int i=0; i<list->n; i++){
            printf("%d \n", *p);
            p++;
        }
    }
}

int main(){
    char choice;
    tlist list;
    list.n = 10;

    list.data[0] = 16;  
    list.data[1] = 17;
    list.data[2] = 18;
    list.data[3] = 19;
    list.data[4] = 20;
    list.data[5] = 21;
    list.data[6] = 22;
    list.data[7] = 23;
    list.data[8] = 24;
    list.data[9] = 25;
    do{
        menu();
        scanf("%s",&choice);
            switch(choice){
                case '1': showList(&list);
                    break;
                case ESC:
                    printf("quiting...\n");
                    break;
                default:
                    printf("Invalid Choice!\n");
                    break;      
            }
    }while(choice != ESC);
    return 0;
}

When I run this program I have this output:

0 17 18 19 20 21 22 23 24 25

I can't understand why the first print is the position of the first element in the array and not the first element itself. Can someone please explain me?

Answer 1

choice is a char and the correct conversion specifier to be used in scanf is c and not s .

One must also be careful when using scanf interspersed with printf statements which print new lines ( \\n ).

When scanf has the conversion specifier c , then it will interpret any whitespace as a character and will not wait for the actual input. So the scanf here should make allowance for the whitespace character by including a leading blank space.

So the scanf statement should be:

scanf(" %c", &choice);

It is also a good practice to check the return value of scanf before proceeding further in the program. As per the standard, scanf returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure.