How to convert lowercase to uppercase and uppercase to lowercase in the same string?

CODE

How to convert lowercase to uppercase and uppercase to lowercase in the same string?

//Write a program to convert lowercase to uppercase and vice versa…

int main()

{

    char a[20];

    int i;

    printf("\n enter string:");

    gets(a);

    for(i=0;a[i]!='\0';i++)

    {

        if(a[i]>64 && a[i]<91)

            a[i]+=32;

        else if(a[i]>96 && a[i]<123)

            a[i]-=32;

    }

    printf("\n new string:%s",a);

}

Output:

enter string: smile GARG

 new string: SMILE garg