We can restrict or allow any character set for user input using scanset  %[].

 

#include <stdio.h>
int main()
{
char str[20];
printf(“Enter any String : “);
scanf(“%[a-z]”,str);
printf(“String you entered is : %s”,str);

return 0;
}

In this program, user input is taken with the help of scanset and it allows only small case characters as input. This means, if user enters any character other than small case characters [a to z], scanf() terminates scanning and only valid part is assigned as input. For example, consider these two outputs :-

Output 1 : 

Enter any String : programmingprashn
String you entered is : programmingprashn
Here, all are small case characters, therefore all characters are scanned and stored in str successfully.

Output 2 : 

Enter any String : programmingPrashn
String you entered is : programming
Here, scanf() stops scanning when it encountered ‘P’, as it does not belongs to the scanset i.e. [a-z].