Use isdigit Function in if statement : If statement « Statement « C Tutorial

#include <stdio.h>
#include <ctype.h>

main()
{

  char cResponse = '\0';

  printf("\nPlease enter a letter: ");
  scanf("%c", &cResponse);

  if ( isdigit(cResponse)== 0 )
    printf("\nThank you\n");
  else
    printf("\nYou did not enter a letter\n");

}

Please enter a letter: 1
      
      You did not enter a letter

6.3.If statement
	6.3.1.	if statement
	6.3.2.	To execute only one statement, opening and closing braces are not required
	6.3.3.	The if statement: a compound statement
	6.3.4.	If with else statement
	6.3.5.	The if-else-if statement
	6.3.6.	if statement with two else statements
	6.3.7.	if statement: compare the value from user input
	6.3.8.	Using nested ifs
	6.3.9.	Use compound conditions to check for upper and lowercase letters
	6.3.10.	Checking for a Range of Values
	6.3.11.	Use isdigit Function in if statement
	6.3.12.	Operators Used in if Comparisons
	6.3.13.	if Comparisons and Their Opposites