How to prevent users from inputting letters or numbers?

Question

I have a simple problem;

Here is the code :

#include
main(){
 int input;
 printf(\"Choose a numeric value\");
 scanf(\"%d\",&input         


        

Answer 1

The strtol library function will convert a string representation of a number to its equivalent integer value, and will also set a pointer to the first character that does not match a valid number.

#include 
#include 
#include 
...
int value;
char buffer[SOME_SIZE];
char *chk;
do 
{
  printf("Enter a number: ");
  fflush(stdout);
  if (fgets(buffer, sizeof buffer, stdin) != NULL)
  {
    value = (int) strtol(buffer, &chk, 10); /* assume decimal format */
  }
} while (!isspace(*chk) && *chk != 0);

If chk points to something other than whitespace or a string terminator (0), then the string was not a valid integer constant. For floating-point input, use strtod.