#include<stdio.h>
#include<string.h>
void main()
{
char str[20];
int i;
printf("Enter the String (Enter First Name) in uppercase : ");
scanf("%s",str);
for(i=0;i<=strlen(str);i++)
{
if(str[i]>=65 && str[i]<=92)
{
str[i]=str[i]+32;
}
}
printf("\nThe String in Lowercase = %s",str);
}
Courtesy: link