Thread: Passing a string to a function - simple question

A simple function that converts lowercase to uppercase.

insert

Code:

This is what was already given:

1	void Cap(char str[]);
2	int main() {
3		char string[31];
4		printf("Enter a string of 30 characters or less: ");
5		scanf("%30[^\n]", string);
6		printf("Capitalized: %s\n", Cap(string));
	}

This is what I wrote:

void Cap(char str[]){
int i=0;
while (str[i]){
if (str[i]>=97 && str[i]<=122){
str[i]-=32;
}
else i++;
}}

======
compiler keeps saying 'invalid use of void expression' in line 6.

You are trying to print the return value of a void function; what do you think should be printed?

Code:

printf("Capitalized: %s\n", Cap(string));

Likely you mean this

Code:

printf("Capitalized: %s\n", string);

Tim S.

So how am I supposed to call the function?

Cap changes the argument you give it. So, at whatever point in time you want string to become capitalized, you should call Cap. Since it doesn't return anything (merely changes the character array), you can't use it in a context of a thing. So: just as you use printf as an action (as opposed to a thing), you should use Cap as an action.

alright guys, thank you for your responses. still cant understand how can i make this piece of code work. if i include it inside main then it works just fine but i am supposed to use an external function for it. and thanks for that notion of thing and action, i find it interesting, have to think about, do more reading and internet research.

Originally Posted by Babkockdood

You could pass a string to Cap() like this: Cap(&string);. Or you could make string a global variable.

Neither... he's got the call more or less correct... it's calling it inside the printf() that's his problem.

To call it inside the printf() he could do this...

Code:

char *Cap(char *str)
{
  int i=0;
  while (str[i])
    if (str[i]>=97 && str[i]<=122)
      str[i]-=32;
    else 
     i++;
return str; }

Thank you tabstop, that solved the problem. I just inserted Cap(string) before printf. And thank you CommonTater but I am not allowed to change the function prototype. I think the teacher wont mind if there's one extra line of code. And thank you all guys.

Originally Posted by vegan

Thank you tabstop, that solved the problem. I just inserted Cap(string) before printf. And thank you CommonTater but I am not allowed to change the function prototype. I think the teacher wont mind if there's one extra line of code. And thank you all guys.

Actually what I wrote is the same as the prototype... I just used a notation I'm more accustomed to. Either str[] or *str should work.