convert lowercase to uppercase

I'm trying to write a programme to convert lowercase to uppercase,


I wrote this myself(phew! wasn't easy)
cpp code

#include<stdio.h>
main()
{
char lett[80];
int convt,i=0;

convt='a'-'A';
printf("Enter the word in lowercase \n");
gets(lett);

for(i=0;(lett[i]>='a')&&(lett[i]<='z');i++)
{
if(lett[i]==' ')
printf("\t");

else lett[i]-=convt;

}

puts(lett);
}

But the problem is, after a space it doesn't convert to uppercase anymore, I've
tried some logic to fix it, (thats why the if statement is there) but it doesn't
work

I got this from the textbook I'm reading. it has the same problem too.


cpp code

#include<stdio.h>
main()
{
char str[80];
int i,delt='a'-'A';
printf("Enter a string less than 80 characters:\n");
gets(str);
i=0;
while(str[i])
{
if ((str[i]>='a')&&(str[i]<='z'))
str[i]-=delt;
++i;
}
printf("The entered string is (in uppercase):\n");
puts(str);
return 0;
}

By the way, the compiler (or software) I use is SILVERFROST(/PLATO);

The way you wrote the 'for' statement is
ingenious, but there's the problem, actually: the
'for' loop executes as long as the condition in
the second part between the parentheses holds.
You wrote: "loop as long as the i-th character in
the string is a lower-case letter." As soon as it
encounters a space (or any other character outside
that range, for that matter), it exits the loop.

What you really want is to loop through *all* the
characters in the string, since you don't know a
priori where the last lower-case character is. In
other words, you want to loop with 'i' varying
from the first index in the string to the last one
(which not necessarily will be 80).