如何用C中的值“删除”数组中的每个元素

Question

I have been trying to solve this problem for about 5 days..can't find any solution please send help. I am supposed to implement a function to "delete" every element in an array by value. Let's say my array is "Hello" and I want to delete every "l". So far I can only delete l once. By the way keep in mind I am not allowed to use pointers for this function...(we haven't learned that yet in my school) Here's my code:

#include <stdio.h>
#include <string.h>

void strdel(char array[], char c);

int main(void)
{
    char source[40];
    printf("\nStrdel test: ");
    strcpy(source, "Hello");
    printf("\nsource = %s", source);
    strdel(source, 'l');
    printf("\nStrdel: new source = %s", source);
    return 0;
}

void strdel(char array[], char c)
{
    int string_lenght;
    int i;
    for (string_lenght = 0; array[string_lenght] != '\0'; string_lenght++) {} 

    for (i = 0; i < string_lenght; i++) {
        if (array[i] == c) {
            for (i = i; array[i] != '\0'; ++i)
                array[i] = array[i + 1];
        }
    }
}

Answer 1

Simple use 2 indexes, one for reading and one for writing. @Carl Norum

void strdel(char array[], char c) {
  int read_index = 0;
  int write_index = 0;
  while (array[read_index] != '\0') {
    if (array[read_index] != c) {
      array[write_index] = array[read_index];
      write_index++;  // Only advance write_index when a character is copied
    }
    read_index++;     // Always advance read_index
  }
  array[write_index] = '\0';
}

The has O(n) performance, much faster than using nested for() loops which is O(n*n).

---

Details:

OP: By the way keep in mind I am not allowed to use pointers for this function.

Note that array in void strdel(char array[], char c) is a pointer, even though it might look like an array.

int for array indexing is OK for learner and much code, yet better to use size_t . int may lack the range needed. Type size_t is an unsigned type that is neither too narrow nor too wide for array indexing needs. This becomes important for very long strings .

Answer 2

Your problem is related to using the variable i in both loops. So once the inner loop is executed, outer loop will terminate right after.

Use another variable for the inner loop.

void strdel(char array[], char c)
{
    int string_lenght;
    int i, j;
    for (string_lenght = 0; array[string_lenght] != '\0'; string_lenght++) {} 

    for (i = 0; i < string_lenght; i++) {
        if (array[i] == c) {
            for (j = i; array[j] != '\0'; ++j)  // Use variable j instead of i
                array[j] = array[j + 1];

           --i;              // Decrement i to "stay" at the same index
           --string_lenght;  // As one character were just removed
        }
    }
}

The above shows how to make OPs approach work. For a better solution see the answer from @chux : https://stackoverflow.com/a/53487767/4386427