Deleting a char and moving it in a string - c

Question

I need ideas for a recursive code that deletes a specific char in a string, and move all the other sting chars together
for Example :
"the weather is cloudy"
the entered char is 'e':
result :
"th wathr is cloudy"
I really don't have any idea how to start, thanks for the help.

Answer 1

#include <stdio.h>
void remove_impl(char* s, char c, char* d) {
if (*s != c) {
*d++ = *s;
}
if (*s != '\0') {
remove_impl(++s, c, d);
}
}
void remove(char* s, char c) {
remove_impl(s, c, s);
}
int main() {
char s[] = "the weather is cloudy";
remove(s, 'e');
puts(s);
}
How it works? Consider remove_impl. s is the original string, c is the character to be deleted from s, d is the resulting string, into which the characters of s, not equal to c, are written. Recursively iterates through the characters of s. If the next character is not equal to c, then it is written in d. The recursion stop point is the condition of checking that the end of s is reached. Since it is necessary to modify the source string, the wrapper is implemented (remove) in which as d, the original string (s) is passed.

Answer 2

An easy way to do it is to loop over the string and add any letter that doesn't match the unwanted letter.
Here's a demonstration:
char *source = "the weather is cloudy";
int source_len = strlen(source);
char *target = (char *)calloc(source_len, sizeof(char));
int target_len = 0;
char to_remove = 'e';
for(int i = 0; i < source_len; i++)
{
if(source[i] != to_remove)
{
target[target_len++] = source[i];
}
}
puts(target); // Output "th wathr is cloudy" in the console

Answer 3

My turn to make a proposal ! I add a assert test and use existing functions (strchr and strcpy).
#include <string.h>
#include <stdio.h>
#include <assert.h>
int removeChar(char *str, char chr)
{
assert(str != 0); // Always control entry !
char *str_pnt = strchr(str, chr);
if (str_pnt) {
strcpy(str_pnt, str_pnt+1);
removeChar(str_pnt, chr);
}
}
void main (void)
{
char str[] = "the weather is cloudy";
char char_to_delete = 'e';
removeChar(str, char_to_delete);
puts(str);
}

Answer 4

This can be done in many ways. What i am thinking right now is store not Allowed char array which going to filter which char should show or not. Something like following..
#include <stdio.h>
#include <string.h>
// Global Scope variable declaration
int notAllowedChar[128] = {0}; // 0 for allowed , 1 for not allowed
char inputString[100];
void recursion(int pos, int len) {
if( pos >= len ) {
printf("\n"); // new line
return;
}
if( notAllowedChar[inputString[pos]]) {// not printing
recursion( pos + 1 , len );
}
else {
printf("%c", inputString[pos]);
recursion( pos + 1 , len );
}
}
int main() {
gets(inputString); // taking input String
printf("Enter not allowed chars:: "); // here we can even run a loop for all of them
char notAllowed;
scanf("%c", &notAllowed);
notAllowedChar[notAllowed] = 1;
int len = strlen(inputString);
recursion( 0 , len );
}
How this work
Lets say we have a simple string "Hello world"
and we want l should be removed from final string, so final output will be "Heo word"
Here "Hello world" length is 11 chars
before calling recursion function we make sure 'l' index which is 108 ascii values link 1 in notAllowedChar array.
now we are calling recursion method with ( 0 , 11 ) value , In recursion method we are having mainly 2 logical if operation, first one is for base case where we will terminate our recursion call when pos is equal or more than 11. and if its not true , we will do the second logical operation if current char is printable or not. This is simply just checking where this char is in notAllowedChar list or not. Every time we increase pos value + 1 and doing a recursion call, and finally when pos is equal or more than 11 , which means we have taken all our decision about printing char or not our recursion will terminate. I tried assign variable with meaningful name. If you still not understand how this work you should go with simple recursion simulation basic ( search in youtube ) and also you should try to manually debug how value is changing in recursion local scope. This may take time but it will be worthy to understand. All the very best.

Answer 5

#include <stdio.h>
/**
* Returns the number of removed chars.
* Base case: if the current char is the null char (end of the string)
* If the char should be deleted return 1 + no of chars removed in the remaining string.
* If it's a some other char simply return the number of chars removed in the remaining string
*/
int removeCAfterwardsAndCount(char* s,char c){
if((*s) == '\0'){
return 0;
}
if((*s) == c){
int noOfChars = removeCAfterwardsAndCount(s+1,c);// s+1 means the remaining string
s[noOfChars] = *s; // move the current char (*s) noOfChars locations ahead
return noOfChars +1; // means this char is removed... some other char should be copied here...
}
else{
int noOfChars = removeCAfterwardsAndCount(s+1,c);
s[noOfChars ] = *s;
return noOfChars ; // means this char is intact ...
}
}
int main()
{
char s[] = "Arifullah Jan";
printf("\n%s",s);
int totalRemoved = removeCAfterwardsAndCount(s,'a');
char *newS = &s[totalRemoved]; // the start of the string should now be originalPointer + total Number of chars removed
printf("\n%s",newS);
return 0;
}
Test Code Here
To avoid moving the chars using loops. I am just moving the chars forward which creates empty space in the start of the string. newS pointer is just a new pointer of the same string to eliminate the empty/garbage string.

Answer 6

#include <stdio.h>
void RemoveChar(char* str, char chr) {
char *str_old = str;
char *str_new = str;
while (*str_old)
{
*str_new = *str_old++;
str_new += (*str_new != chr);
}
*str_new = '\0'; }
int main() {
char string[] = "the weather is cloudy";
RemoveChar(string, 'e');
printf("'%s'\n", string);
return 0; }

Answer 7

#include <stdio.h>
#include <string.h>
char *remove_char(char *str, int c)
{
char *pos;
char *wrk = str;
while((pos = strchr(wrk, c)))
{
strcpy(pos, pos + 1);
wrk = pos;
}
return str;
}
int main()
{
char str[] = "Hello World";
printf(remove_char(str, 'l'));
return 0;
}
Or faster but mode difficult to understand version:
char *remove_char(char *str, int c)
{
char *pos = str;
char *wrk = str;
while(*wrk)
{
if(*wrk == c)
{
*wrk++;
continue;
}
*pos++ = *wrk++;
}
*pos = 0;
return str;
}
Both require the string to be writable (so you cant pass the pointer to the string literal for example)