如何在C中输入和扫描多个字符

Question

I want to enter multiple printfs but i dont get opportunity to enter. I can enter only 1, but after that it just ends the programme.I tried with do while but it didnt work

int main()
{
  int number;
  char username[30]="";
  char fullName[30]="";
  char password[30]="";
  printf("Do you want to log in(1) or register (2)? \n");  
  scanf("%d",&number);
  if (number==2)
  {
    printf("username : ");
    scanf("%s",&username);
    printf("Full name : ");
    scanf("%s",&fullName);
    printf("Password : ");
    scanf("%s",&password);
    printf("Repeat password : ");
    scanf("%s",&password);
  }
  return 0;
}

Answer 1

Read full lines using fgets() into a suitably large buffer, then parse that.

Note that %s will stop at the first blank character, so a full name of "Mr X" will leave "X" in the input buffer, grabbing that for the password and so on. It's really not a robust way of getting input.

Answer 2

I can enter only 1, but after that it just ends the programme.

Of course, as the code has if (number==2) @Scadge

If you enter "2" , consider the following:

---

scanf("%s",&fullname); will not save spaces or other white-spaces into fullname . Entering a full name like "John Doe" will save "John" into fullname and "Doe" into password .

Avoid using scanf() .

---

Rather than use scanf() to read user input, read user input with fgets() . This is a fine opportunity for helper functions that can handle various input issues.

int read_int(const char *prompt) {
  if (prompt) fputs(prompt, stdout);
  fflush(stdout);  // insure output is written before asking for input

  char buffer[40];
  if (fgets(buffer, sizeof buffer, stdin) == NULL) {
    return NULL;
  }

  int i;
  if (sscanf(buffer, "%d", &i) == 1) {
    return i;
  }

  // TBD - what should code do if invalid data entered.  Try again?
}

char *read_line(char *dest, sizeof size, const char *prompt) {
  if (prompt) fputs(prompt, stdout);
  fflush(stdout);  // insure output is written before asking for input

  char buffer[size * 2 + 1];  // form buffer at _least 1 larger for \n
  if (fgets(buffer, sizeof buffer, stdin) == NULL) {
    return NULL;
  }

  size_t len = strlen(buffer);
  if (len > 0 && buffer[len-1] == '\n') buffer[--len] = '\0';

  if (len >= size) {
    // input too big - how do you want to handle this?
    TBD_Code();
  } 
  return strcpy(dest, buffer);
}

Now use these 2 helper functions for clean user input

// printf("Do you want to log in(1) or register (2)? \n");  
// scanf("%d",&number);
number = read_int("Do you want to log in(1) or register (2)? \n");

...

// printf("username : ");
// scanf("%s",&username);
read_line(username, sizeof username, "username : ");
// printf("Full name : ");
// scanf("%s",&fullName);
read_line(fullName, sizeof fullName, "fullName : ");

Additional code could be added to check for end-of-file, extremely long lines, int range testing, etc.

Answer 3

Use c library function fgets().

#include <stdio.h>
int main(){
     Char username[10];
     printf(“Username: “);
     fgets(username,10,stdin);
}