insert a particular char into the string - c

Question

for ex: if the string="EXAM"
insert a char'x' after every char of a string
output must be string="EXXXAXMX".i have done program for that but i stored a string and then i inserted 'x'.but i want the pgm to get input string from user and insert a char 'x' after every char of that string.how to do it?
#include<stdio.h>
#include<conio.h>
#include<string.h>
void strexpand(char [],char []);
void main()
{
char name[]="EXAM";
int length;
clrscr();
length=strlen(name);
printf("\n\tName=%s Length=%d",name,length);
strexpand(name);
getch();
}
void strexpand(char name[])
{
int i;
while(name[i]!='\0')
{
i++;
}
if(name[i]=='\0')
{
name[8]=name[4];
name[6]=name[3];
name[4]=name[2];
name[2]=name[1];
name[1]='x';
name[3]='x';
name[5]='x';
name[7]='x';
printf("\n\n\tAltered string is=%s",name);
}
}

Answer 1

It should be something like this , the new string will be always 2 times bigger than the original , so we should allocate it as 2 times bigger string , and then just copy as i said on comments.
char* strexpand(char name[])
{
int length=0;
int i=0 ,j=0;
char* retValue =null;
while(name[length]!='\0')
{
length++;
}
length++;
retValue = malloc (sizeof(char* length * 2));
if(!retValue)
return null;
for(i=0;i<length;i++,j+=2)
{
retVal[j] = name[i];
retVal[j+1] = 'x';
}
//at this point j did got +=2
retVal[j] = '\0';
return retVal;
}

Answer 2

Fix
#include<stdio.h>
#include<conio.h>
#include<string.h>
void strexpand(char []);
void main()
{
char name[9];
strcpy(name, "EXAM");
int length;
length=strlen(name);
printf("\n\tName=%s Length=%d",name,length);
strexpand(name);
getch();
}
void strexpand(char name[])
{
int i=0;
while(name[i]!='\0')
{
i++;
}
if(name[i]=='\0')
{
name[7]=name[3];
name[5]=name[2];
name[3]=name[1];
name[1]=name[0];
name[0]='x';
name[2]='x';
name[4]='x';
name[6]='x';
name[8] = '\0';
printf("\n\n\tAltered string is=%s",name);
}
}
note1: This code assumes that the string has at most has 8 characters.
note2: Arrays are indexed from 0. The first element is array[0]
note3: the line name[8] = '\0'; takes care of closing the string since C strings are null-terminated. It is important to know that to store n chars in a C string you always need n+1 bytes.
Some explanation
void strexpand(char name[])
{
int i;
while(name[i]!='\0')
{
i++;
}
This part is problematic, becasue i will have some junk value. It should be
void strexpand(char name[])
{
int i = 0;
while(name[i]!='\0')
{
i++;
}
Also when using strexpand you assue that its parameter has at least 9 elements because of this line:
name[8]
When you give it a smaller string than 9 elements (as in your code) the code will try to access elements outside of allocated space, which will result in a segfault.
So, when you called it with "EXAM" the parameter looked like this in memory:
['E','X','A','M','\0']
Given this, name[5] was already problematic.