Caesar Cipher - Program in C

#include<stdio.h>
#include<stdlib.h>
char*plainTextToCipherText(char plainText[],int n)
{
 char *cipherText;
 int i;
 cipherText=(char*)malloc(sizeof(char)*1000);
 for(i=0;plainText[i];i++)
 {
  if(plainText[i]!=' ')
   cipherText[i]=((plainText[i]-'a'+n)%26)+'a';
  else
   cipherText[i]=plainText[i];
 }
 cipherText[i]='\0';
 return cipherText;
}
char*cipherTextToPlainText(char cipherText[],int n)
{
 char *plainText,c;
 int i;
 plainText=(char*)malloc(sizeof(char)*1000);
 for(i=0;cipherText[i];i++)
 {
  if(cipherText[i]!=' ')
  {
   c=(cipherText[i]-'a'-n)%26;
   if(c<0)
    c+=26;
   c+='a';
   plainText[i]=c;
  }
  else
  {
   plainText[i]=cipherText[i];
  }
 }
 plainText[i]='\0';
 return plainText;
}
int main()
{
 int n;
 char plainText1[1000],*cipherText1,cipherText2[1000],*plainText2;

 // Encoding Cipher Text
 printf("Enter the Plain Text (in lower case): ");
 scanf(" %[^\n]s",plainText1);
 printf("Enter the number of characters to be shifted : ");
 scanf("%d",&n);
 cipherText1=plainTextToCipherText(plainText1,n);
 printf("Cipher Text is : %s\n",cipherText1);


 // Decoding Plain Text
 printf("\nEnter the Cipher Text (in lower case) : ");
 scanf(" %[^\n]s",cipherText2);
 printf("Enter the number of charaters to be shifted : ");
 scanf("%d",&n);
 plainText2=cipherTextToPlainText(cipherText2,n);
 printf("The Plain Text is : %s\n",plainText2);
 return 0;
}