C program to convert lower case to upper case and upper case to lower case

Lower case to upper case :-
#include<stdio.h>
#include<conio.h>
void main()
{
char a[100];
int i=0;
puts("Enter the string in lower case");
scanf("%s",a);
printf("Lower case :- %s\n",a);
printf("Upper case :- ");
while(a[i]!='\0')
{
printf("%c",a[i]-32);
i++;
}
}

Upper case to lower case :-
#include<stdio.h>
#include<conio.h>
void main()
{
char a[100];
int i=0;
puts("Enter the string in upper case");
scanf("%s",a);
printf("Upper case :- %s\n",a);
printf("Lower case :- ");
while(a[i]!='\0')
{
printf("%c",a[i]+32);
i++;
}
}