Thread: beginner help with C (pointers)

I am a C beginner. I just created a program that iterates over the length of a string that calls toupper() on each character.

My question: I want to create a copy of the original, translate that and then return a pointer to the translated copy... and I am having troubles.

Anyone up for helping?

Thanx.

i can't help if you don't show your code and explain what the problem is.

Originally Posted by Meldreth

i can't help if you don't show your code and explain what the problem is.

ok sry, I am also on a mac. This is the code:

Code:

#include <stdio.h>

main()
{
        char firstname[80];
        int loop =0;

        printf(" Enter your name in lowercase letters: \n");
        scanf(" %s", firstname);
        for(; firstname[loop] != 0; loop ++ )
                firstname[loop] = toupper(firstname[loop]);

        printf("Your name in uppercase letters is: %s\n", firstname);
}

There aren't any problems, i just want to learn how to use the function of toupper() in a fancier way. A friend said i could have it create a copy of the original, translate that and then return a pointer to the translated copy... but as a beginner I am confused by this. Friend is currently out of pocket.

as a beginner, that coding does not flow easily. Will you repost with comments about what each line does? I want to avoid anything needing ctype.h because with my mac working in terminal, many functions are not part of the standard.

I cannot get code to compile:

Code:

$ gcc -o caps caps.c
caps.c: In function ‘supper’:
caps.c:10: error: syntax error before ‘{’ token
caps.c:31: error: syntax error before ‘for’

I would love to understand what yall are talking about, can you post with a more kindergarten style so the beginner can learn?

Code:

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

char *sdup(char* s);
char *supper(char *s)

int main()
{
    char s[80], *p;
    printf("enter a string> ");
    fgets(s, 80, stdin);
    fputs(s, stdout);
    p = supper(s);
    fputs(p, stdout);
    free(p);
    return EXIT_SUCCESS;
}

char *sdup(char* s)
{
    char *p = malloc(strlen(s)+1);
    return strcpy(p, s);
}

char *supper(char *s)
{
    char *p = strdup(s);
    int i;
    for(i = 0; p[i]; i++)
        p[i] = toupper(p[i]);
    return p;
}

after trying to complie:

Code:

$ gcc -o caps caps.c
caps.c: In function ‘supper’:
caps.c:10: error: syntax error before ‘{’ token
caps.c:31: error: syntax error before ‘for’

your code is already kindergarten style. you asked for something fancier, and that's what malloc does for you. i also fixed the code in my first post, so you can try it again.

ok noted the error in yalls replys. fixed and it compiles.. but i still don't unerstand why. can you add comments describing what each line preforms?

im not asking for kindergarten code, im asking for you to explain what the code does to me as a beginner.

Originally Posted by likewise

can you add comments describing what each line preforms?

yes i can.

Code:

#include <stdio.h>  /* pastes contents of stdio.h to here */
#include <stdlib.h> /* pastes contents of stdlib.h to here */
#include <string.h> /* pastes contents of string.h to here */
#include <ctype.h>  /* pastes contents of ctype.h to here */
/* blank line */
char *sdup(char* s); /* declares a function called sdup */
char *supper(char *s); /* declares a function called supper */
/* blank line */
int main() /* definition of main */
{ /* opening curly brace */
    char s[80], *p; /* declare an array of 80 char and a pointer to char */
    printf("enter a string> "); /* print something cool */
    fgets(s, 80, stdin); /* make the user type a string, up to 80 characters */
    fputs(s, stdout); /* print the string the user typed */
    p = sdup(s); /* make a copy of the string the user typed */
    fputs(supper(p), stdout); /* convert the copy to upper case and print it */
    free(p); /* let the dynamic memory go back to the process */
    return EXIT_SUCCESS; /* return succes */
} /* closing curly brace */
/* blank line */
char *sdup(char* s) /* definition of sdup, copies strings */
{ /* opening curly brace */
    char *p = malloc(strlen(s)+1); /* dynamically allocate strlen(s)+1 bytes */
    return strcpy(p, s); /* copy the string contained by s into the memory at p and return it */
} /* closing curly brace */
/* blank line */
char *supper(char *s) /* definition of supper, copies a string to upper case */
{ /* opening curly brace */
    char *p = sdup(s); /* copy the string s */
    int i; /* int i */
    for (i = 0; p[i]; i++) p[i] = toupper(p[i]); /* convert the string to upper case */
    return p; /* return the copy */
} /* closing curly brace */