C program to convert given upper case letters to lower case

This C program will convert given uppercase letters into lover case.

#include<stdio.h>
#include<string.h>
int main()
{
  char str1[10]="ABCD";
  int i;
  for(i=0; i<4; i++)
  {
    printf("%c",str1[i]+32);
  }
  return 0;
}

Output of the program:

abcd