How to deal with wrong input C?

Question

beginners question: Imagine this scenario: I request the user to enter an integer (getting it by using scanf) but the user enters a character, because of that the program reaches it's end... but I want to overcome it, and make the program tell him that he has provided invalid input and give the user another chance to enter an input, how can I do that?

Answer 1

Use fgets(), then sscanf() or strtol().

int number;
char ch;
char *Prompt2 = "":
do {
  printf("%sEnter number :", Prompt2);
  Prompt2 = "Invalid input\n";  // Change Prompt2 
  buffer char[50];
  if (fgets(buffer, sizeof buffer, stdin) == NULL) {
    Handle_EOF();
  }  
} while (sscanf(buffer, "%d %c", &number, &ch) != 1);

Using strtol() instead of sscanf() adds +/- overflow protection as that sets errno.

  char *endptr; 
  errno = 0;
  long number = strtol(buffer, &endptr, 10);
  if (errno || buffer == endptr || *endptr != '\n') Handle_Error(();

See Read_long() as an example of how to use this a function.

Answer 2

The return value of scanf is the number of arguments successfully scanned.

Answer 3

How about:

  int n;
  int c;
  printf("Please enter an integer: ");
  while (scanf("%d", &n) != 1) {
    while (!isspace(c = getchar()));
    ungetc(c, stdin);
    printf("You must enter a valid number. Try again.\n");
    continue;
  }