c - Why isn't my removeString function removing the characters? -

i'm working through exercise in book, i'm not allowed use library functions aside printf , scanf.

i have written program takes in string. can input how many characters remove string. , choose @ index, performed.

my attempt @ loop through characters want keep @ end of function , replace them functions want lose.

for reason doing exact opposite.

if input string: "the wrong son" , choose remove 6 characters , begin @ 4th index of array,

i should get: "the son"

instead, getting "the wro".

i have been banging head against 4 hours now.

can please tell me i'm going wrong?

#include <stdio.h>  void removestring(char source[], int start, int count); int stringlength(const char string[]);      int main(void)     {         int start, count;         char source[20];           printf("what's string?\n");         scanf("%[^\n]s", source);          printf("how many characters want remove?\n");         scanf("%i", &count);          // choose index start deletion         printf("where starting from?\n");         scanf("%i", &start);          // call function remove characters string         removestring(source, start, count);          // print out result, stored in source         printf("here's result: %s\n", source);          return 0;     }      void removestring(char source[], int start, int count)     {         int i, j;          // find length of string         int length = stringlength(source);           //loop through last few characters want keep until hit end of string          for(i = (start+count); <= length; i++)         {             //loop backwards through string, first of ones want keep, stop @ 'start' of index             for(j = (start+count)-1; j <= start; j--)             {                 // assign 'i' last few characters want keep , put them in place of characters want delete                 source[j] = source[i];             }         }          // assign null character end string once we've finished modifying         source[count + 1] = '\0';     }      int stringlength(const char string[])     {         int count =0;          while(string[count] != '\0')             count++;          return count;     } 

can please tell me i'm going wrong?

in indexing.

instead of posting simple solution, try make understand went wrong.

for(i = (start+count); <= length; i++) 

here, input 'the wrong son', length equal 13. result indexing source[13], not out-of-bounds access, since have statically initialize array 20 cells, it's still exceeding length of input string 1.

so change i < length.

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now loop:

for(j = (start+count)-1; j <= start; j--)  

it says start 9 (for example input) , decrease j until it's less or equal 4, doesn't make sense, meant write:

j >= start

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now grab piece of paper , write down input , pointers please:

start = 4 count = 6 length = 13         start    start+count          |           |          v           v |t|h|e| |w|r|o|n|g| |s|o|n|  0 1 2 3 4 5 6 7 8 9 101112 

run algorithm now.

you getting i-th character , overwrite j-th ones, that's why end 'the nnn' after applying fixes, right?

so want go until start plus have overwritten , should not overwrite again!

as result, change this:

j >= start

to

j >= start + - (start + count); 

and should output:

c02qt2ubfvh6-lm:~ gsamaras$ ./a.out what's string? wrong son how many characters want remove? 6 starting from? 4 here's result: son 

if that's not case, tell me post whole fixed code.

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edit:

my appending of '\0' wrong?

no, it's correct (after @ least fixes proposed in answer). let's check code:

printf("source = %s\n", source); printf("count = %d\n", count); printf("source[count] = %c\n", source[count]); printf("source[count + 1] = %c\n", source[count + 1]); source[count + 1] = '\0'; 

which gives:

source = sonnnnson count = 6 source[count] = n source[count + 1] = n 

so count + 1 equal 7, second 'n' in string, want place null terminator.