The result box is a problem due to a gap? - c

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 100
typedef struct person {
char name[SIZE];
char address[SIZE];
char mobilephone[SIZE];
char desc[SIZE];
} PERSON;
void menu();
PERSON get_record();
void print_record(PERSON data);
void add_record(FILE* fp);
void search_record(FILE* fp);
void update_record(FILE* fp);
void delete_record(FILE* fp);
int main(void)
{
FILE* fp;
int select;
printf("Enter an integer value: ");
if ((fp = fopen("address.dat", "a+")) == NULL) {
fprintf(stderr, "I can't open the file for input.");
exit(1);
}
while (1) {
menu();
printf("Enter an integer value: ");
scanf_s("%d", &select);
switch (select) {
case 1: add_record(fp); break;
case 2: update_record(fp); break;
case 3: search_record(fp); break;
case 4: delete_record(fp); break;
case 5: return 0;
}
}
fclose(fp);
return 0;
}
void menu()
{
printf("====================\n");
printf(" 1. Additional\n 2. correct\n 3. Search\n 4. elimination\n 5. Termination\n");
printf("====================\n");
}
void search_record(FILE* fp)
{
char name[SIZE];
PERSON data;
fseek(fp, 0, SEEK_SET);
fflush(stdin);
printf("The name of the person you want to explore");
gets_s(name, SIZE);
while (!feof(fp)) {
fread(&data, sizeof(data), 1, fp);
if (strcmp(data.name, name) == 0) {
print_record(data);
break;
}
}
}
As shown in the picture above, entering an integer ignores entering the name and returns to the menu.
Why does this phenomenon appear?
If you press 3 and press the enter, the direction of the function for 3 cannot proceed, and there is a problem of returning to the menu as if it were entered twice in a row.
If this problem is solved, how should we solve it?
enter image description here

Answer 1

Scanf only consumes what you tell it to, leaving the rest in stdin. Gets stops at the first instance of newline or a terminating character.
Your input is "3\n" (newline happens when you press enter). Your scanf pattern consumes the first integer and stops at the first non-numerical character (roughly). In this case that is '\n'. So when you call gets, it immediately consumes the newline left on stdin by scanf and seems to "skip" that input.
fflush(stdin) before taking an input (either scanf or gets) to drop leftover stuff.
Something to think about in the future would be: is the input "3foo\n" still valid? As I mentioned, scanf only reads what you tell it to. So the "foo\n" is ignored by the scanf pattern "%d". Further, the l33t input of "0n3\n" is interpreted as zero despite the user's intention.