Change string to upper case without strupr 

#include<stdio.h>
void upperString(char*);
main()
{
char string[100];
   printf("Enter a string to convert it into upper case\n");
gets(string);
   upperString(string);
   printf("Entered string in upper case is \"%s\"\n", string);
   return 0;
}
void upperString(char *string)
{
while(*string)
{
if ( *string >= 'a' && *string <= 'z' )
{
*string = *string - 32;
}
string++;
}
}

Change string to lower case without strlwr
#include<stdio.h>
void lowerString(char*);
main()
{
char string[100];
   printf("Enter a string to convert it into lower case\n");
gets(string);
   lowerString(string);
   printf("Entered string in lower case is \"%s\"\n", string);
   return 0;
}
void lowerString(char *string)
{
while(*string)
{
if ( *string >= 'A' && *string <= 'Z' )
{
*string = *string + 32;
}
string++;
}
}