Write a program to read a sentence and replace lowercase characters by uppercase and vice-versa

Write a program to read a sentence and replace lowercase characters by uppercase and vice-versa

1. #include<stdio.h>
2. #include<string.h>
3. void main()
4. {
5.     char str[100];
6.     char ch;
7.  
8.     int len;
9.     printf("Input the string: ");
10.     gets(str);
11.     len=strlen(str);
12.  
13.     for(int i=0; i<len; i++) {
14.         ch = (islower(str[i])?toupper(str[i]):tolower(str[i]));
15.     printf("%c", ch);
16.     }
17. }