String Conversion

[gsoft]

Im having a bit of trouble converting a string to lower case then to upper case.

#include <stdio.h>
#include <string.h>

int main(void)
{
	
	char buf[80], *ptr, *string;
	
	while (1)
	{
		
		puts("Enter a line of text, a blank to exit.");
		fgets(buf, sizeof buf, stdin);
		
		if ((ptr=strchr(buf,'\n'))!=NULL)
			*ptr='\0';
		
		if (strlen(buf)==0)
			break;
		
		string = buf;
		
		tolower(string);
		puts(buf);
		toupper(string);
		puts(buf);
		
	}
	
	return 0;
	
}

The only error is

upper.c:32:2: warning: no newline at end of file

Line 32 is the last brace.

[edit]
If its any help I am using gcc
[/edit]

[sean]

It's nothing big. Just go to line 32 and press 'Enter'. I don't know why that causes a problem...

[gsoft]

Ok that stopped the error however the strings arent being converted say if I typed testing

the first show is

testing - which is correct

then for upper case
testing - which is suppose to be TESTING

[Brian]

for (int i = 0; buf[i] != '\0'; i++) {
    buf[i] = toupper(buf[i]);
}

[gsoft]

Thanks Brian that worked a charm. So from viewing that toupper and tolower only take one character at a time?

[sean]

Correct.

[Emmanuel Delaha]

Im having a bit of trouble converting a string to lower case then to upper case.

#include <stdio.h>
#include <string.h>

int main(void)
{
	
	char buf[80], *ptr, *string;
	
	while (1)
	{
		
		puts("Enter a line of text, a blank to exit.");
		fgets(buf, sizeof buf, stdin);
		
		if ((ptr=strchr(buf,'\n'))!=NULL)
			*ptr='\0';
		
		if (strlen(buf)==0)
			break;
		
		string = buf;
		
		tolower(string);
		puts(buf);
		toupper(string);
		puts(buf);
		
	}
	
	return 0;
	
}

If its any help I am using gcc

Clearly your gcc calling is too lax. Add this:

-W  -Wall  -ansi  -O2

and you will get that:

main.c: In function `main':
main.c:23: warning: implicit declaration of function `tolower'
main.c:25: warning: implicit declaration of function `toupper'

That denotes the lack of prototypes for the quoted functions. Actually, an include of <ctype.h> is missing.

Once fixed, the things become more obvious:

main.c: In function `main':
main.c:24: warning: passing arg 1 of `tolower' makes integer from pointer without a cast
main.c:26: warning: passing arg 1 of `toupper' makes integer from pointer without a cast

Of course, your code is wrong, because you passed an address to an int parameter. The tolower()/toupper() functions only process one character, as written into your C-book...

Lesson of the day
- Teach your compiler to tell the truth
- Fix your code the right way until you have no errors or warnings (typecast is not the right way).
- Read you manual before using a new function.

A working solution have been given in this thread.

[gsoft]

Hmm Ok i guess I learnt something about my Compiler thanks. Ill go over my other small programs ive made to see if they work.

[gsoft]

Ok may I ask one question why cannot I not use

// for comments ? gcc says

error: syntax error before '/' token

However when I change it to /* */ it works, I thought // was added in the new C99 version of ANSI C.

[Emmanuel Delaha]

Ok may I ask one question why cannot I not use

// for comments ? gcc says
However when I change it to /* */ it works, I thought // was added in the new C99 version of ANSI C.

Yes, but your compiler is probably working in C90 mode. You can try to replace -ansi by -std=c99, but I don't recommend it because (debatable):

- It's ugly
- It trends to add comments at the end of the lines that makes the code unreadable and unpritable without wrapping (ugly too).
- Most of the compilers are still C90 and don't support the C99 comments, specially on embedded systems (the playyard of the C-language)

[gsoft]

Thank you very much you have been a terrific help