strlwr, strupr in c

stwlwr in c

#include<stdio.h>
#include<string.h>

int main()
{
    char string[] = "Strlwr in C";
    
    printf("%s\n",strlwr(string));
    
    return  0;
}

strupr in c

#include<stdio.h>
#include<string.h>

main()
{
    char string[] = "strupr in c";
    
    printf("%s\n",strupr(string));
    
    return  0;
}

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++;
   }
}