Insertion and deletion operations on strings

[mathware]

I need help with the following program:

code:

#include<stdio.h> #include<stdlib.h> #include<string.h>   typedef struct {     char *str; }STRING;   //initializes dynamic string void init(STRING *s) {     char str[10];     s->str=(char *)calloc(strlen(str)+1,sizeof(char));     strcpy(s->str,str); }   //appends a character at the end of STRING void append_c(STRING *s,char c) {     int capacity=10,used=0;     s->str=(char *)malloc((capacity+1)*sizeof(char));     int i;     for(i=0;i<1;i++)     {        if(used == capacity+1)        {            capacity=capacity*2;            s->str=(char *)realloc(s->str,sizeof(char) * (capacity+1));        }        s->str[used]=c;        s->str[used+1]=0;        used++;     } }   //concatenates string 'str' to STRING void append_s(STRING *s,char *str) {     init(s);     strcat(s->str,str); }   //inserts the string 'str' to STRING at position 'pos' //'pos' is valid if 0<=pos<=strlen(STRING) //if pos<0 then set pos=0 //if pos>strlen(STRING) then set pos=strlen(STRING) void insertion(STRING *s,int pos,char *str) {     char *temp;     int len=0;       init(s);     for(; s->str; temp++)         len++;     int len2=strlen(str);     temp=(char *)malloc((len+len2+2) * sizeof(char));       if(pos < 0)         pos=0;     else if(pos > len)         pos=len;       strncpy(temp,s->str,pos+1);     temp[pos+1]=0;     strcat(temp,str);     strcat(temp,s->str+pos+1);   }   //removes 'n' characters from STRING starting from 'pos' //0<=pos<=strlen(STRING) //if n > remainder to the right then removes all remaining characters void deletion(STRING *s,int pos,int n) {     char *temp;     int len=0;       init(s);     for(; s->str; temp++)         len++;     temp=(char *)malloc((len+1) * sizeof(char));       if(pos < 0 || pos > len)         return;     int x=len-pos;       if(n <= x){     strncpy(temp,s->str,pos);     temp[pos]=0;     strcat(temp,s->str+pos+n);}       else{     strncpy(temp,s->str,pos);     temp[pos]=0;} }     int main() {     STRING s;     init(&s);       append_s(&s,"GRAMMING");     printf("%s\n",s.str);       insertion(&s,0,"PRO");     printf("%s\n",s.str);       insertion(&s,12,"L");     printf("%s\n",s.str);       append_c(&s,'A');     printf("%s\n",s.str);       append_s(&s,"NGUAGES");     printf("%s\n",s.str);       deletion(&s,1,4);     printf("%s\n",s.str);       free(s.str);       return 0; }

Output should be:

code:

//GRAMMING //PROGRAMMING //PROGRAMMING L //PROGRAMMING LA //PROGRAMMING LANGUAGES //PAMMING LANGUAGES

Functions for insertion and deletion don't work.
Could someone correct possible syntax and logical errors?