C Newbie: Help with Simple Function -

spoiler: absolute beginner c. threw threw program test knowledge, compiler giving me errors. problem , why?

#include <stdio.h>  void main() {     char *string = "abcdefghi";      printf("%s\n\n", string);      printf("%s\n\n", substr(string, 1, 2)); }  char * substr(char *string, int start, int length) {     int i;     char *temp;      for(i = 0; < length; i++)     {         temp[i] = string[i+start];     }      return temp; } 

edit:

sorry, it's 1 here, i've been trying figure out.

the errors are:

main.c: in function ‘main’: main.c:9: warning: format ‘%s’ expects type ‘char *’, argument 2 has type ‘int’ main.c: @ top level: main.c:12: error: conflicting types ‘substr’ 

here errors see:

use of uninitialized pointer

in substr declare char *temp; , use without initializing anything. not compile-time error, program crash when run it, since temp point random memory address. case of undefined behavior, , c chock full of it. undefined behavior come out of , eat pets if aren't careful.

consider malloc()ing memory, or having function receive pointer buffer can write portion of string.

use of function not yet declared

in c must declare functions before used, or @ least declare prototype. above main()'s declaration, add line:

char * substr(char *string, int start, int length); 

no use of const makes sense

when assigning string literal char*, variable should declared const. change

char *string = "abcdefghi"; 

to

const char *string = "abcdefghi"; 

you have change function prototype to

char * substr(const char *string, int start, int length) 

which should have been in first place.

added 2010-12-02:

substr() not add terminating null character

the substr() function, while algorithmically correct in every other sense, not add terminating null character new string. cause printf() , every other string-using function (like strlen(), strcpy(), etc.) run off end of string unallocated heap memory, or stack memory (depending on how resolve "uninitialized pointer" issue).

to fix this, add line after for loop, , before return statement:

temp[i] = '\0'; 

note should not added in loop, have effect of creating string 0 length.