C Exercises: Remove all whitespace from a string

C Callback function: Exercise-7 with Solution

Write a C program to remove all whitespace from a string using a callback function.

Sample Solution:

C Code:

#include <stdio.h>

#include <string.h>

#include <ctype.h>

void remove_whitespace(char * str, void( * modify)(char * )) {
  int i, j = 0;
  for (i = 0; str[i] != '\0'; i++) {
    if (!isspace(str[i])) {
      str[j] = str[i];
      j++;
    } else {
      modify( & str[i]);
    }
  }
  str[j] = '\0';
}
void remove_space(char * ch) {
  * ch = '\0';
}
int main() {
  char str[100];
  printf("Enter a string: ");
  fgets(str, sizeof(str), stdin);
  str[strcspn(str, "\n")] = '\0'; // remove the newline character
  printf("Original string: %s\n", str);

  // remove whitespace using callback function
  remove_whitespace(str, remove_space);

  printf("String without whitespace: %s\n", str);

  return 0;
}

Sample Output:

Enter a string: example .  com
Original string: example .  com
String without whitespace: example.com

Explanation:

In the above example 'remove_whitespace' function takes a string str and a function pointer modify as arguments. It loops through each character of the string using a for loop. If the current character is not a whitespace character (determined using the isspace function from the ctype.h library), it copies the character to the output string at position j and increments j.

If the current character is a whitespace character, it calls the modify function with a pointer to the current character.

The 'remove_space' function is the callback function that modifies each whitespace character. It simply replaces the whitespace character with a null character ('\0'), effectively removing it from the string.

The main() function reads a string from the user using fgets() function and removes the newline character at the end of the string using strcspn and assignment of '\0'. It then calls remove_whitespace with the input string and the remove_space callback function. Finally printf() function prints the modified string without whitespace.

Flowchart:

C Programming Code Editor:

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