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× C Standard Library

The C <ctype.h> isdigit() function is used to check if the given character is a decimal digit or not. Decimal digits are one of the 10 digits: 0123456789.


int isdigit ( int ch );               


ch Specify the character to be checked, casted to an int, or EOF.

Return Value

Returns non-zero value (i.e, true) if ch is a decimal digit, else returns zero (i.e, false).


The below example shows the usage of isdigit() function.

#include <stdio.h>
#include <ctype.h>
int main (){
  char str[50] = "980Alpha55";

  //counting the numbers of 
  //decimal digits in str
  int i = 0, count = 0;
  while(str[i]) {

  //displaying the output
  printf("%s contains %d decimal digits.", str, count);  
  return 0;

The output of the above code will be:

980Alpha55 contains 5 decimal digits.

❮ C <ctype.h> Library