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).

Code:

#include<stdio.h>
#include<conio.h>

void main()
{
 char arr[80];
 int diff,i;
 clrscr();
 diff='a'-'A';
 printf("\nenter a string= ");
 gets(arr);
//scanf("%s",arr);

 for(i=0;arr[i]!='\0';i++)
 {
  if(arr[i]>='a' && arr[i]<='z')
    arr[i]-= diff;
  else if(arr[i]>='A' && arr[i]<='Z')
    {}
  else if(arr[i]==' ')
    printf("\t");
  else
    {}
  }
 puts(arr);
 //printf("\nthe upper case converted strins is =%s",arr);
 getch();

}