Please help! I get a "conflicting types for" error.

[hotshotennis]

Here is my code so far: (not a complete program)

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

#define MAX 81

FILE *fileOpen(char fileName[]);
int readFile(FILE* inputFile);

int checkCreditCard(char *strng);
int digitsOnly(char *strng);
int checkLastDigit(char *strng);


int main (void)
{

FILE *inputFile;
char fileName[MAX];



inputFile = fileOpen(fileName);
readFile(inputFile);

char *strng;
checkCreditCard(strng);
fclose(inputFile);
return 0;
}

FILE * fileOpen(char fileName[]) //function A
{
FILE *inputFile;


       printf("Please enter a file name.\n");
       scanf("%s", fileName);

        inputFile = fopen(fileName, "r");
        if (!inputFile){
        printf("\aCould not open the input file.\n");
        exit (1);
       }

       return inputFile;

}
int readFile(FILE* inputFile) //function B
{

 char strng[MAX];
 int len;


       fgets(strng, sizeof(strng), inputFile);
       len = strlen(strng);
       if (strng[len - 1] == '\n'){
               strng[len - 1] = '\0';
       }
       while(fgets(strng, sizeof(strng), inputFile)){

           fgets(strng, len, inputFile);

       }
       return 0;



}

int checkCreditCard(char* strng)// Function C
{
int strlen(char* strng);
int len;
if (len != 16)
{
       return 0;
}
return 1;
digitsOnly(strng);
}
int digitsOnly(char *strng)// Function F
{
int i;

for (i=0; strng [i] != '\0'; i++){
       if(!isdigit(strng[i]))
               return 0;
}

return 1;
}

-When I compile it, it tells me "conflicting types for 'strlen'. I don't know how to resolve this. Please help! Let me know if you need more information. This is for a homework assignment. Thank you for your time.

[GReaper]

int strlen(char* strng);

What's this line supposed to do inside your "checkCreditCard()" function?

And why is everything purple?!

[hotshotennis]

int strlen(char* strng);

What's this line supposed to do inside your "checkCreditCard()" function?

And why is everything purple?!

-I'm trying to check the length of a string from a file and make sure that it is exactly 16 characters. We were told to use strlen for this. This is my interpretation of this. Not sure how to make it work...

-Sorry, I didn't realize that it was all purple... It doesn't look purple from my screen, all the text is black... I'm writing the program in UNIX vi editor and then emailing it to myself so that I can copy and paste it here... that might be why. But it looks fine to me.

[GReaper]

Anyway, your problem is that you try to redeclare "strlen()", that's why your compiler is complaining. You don't need to, because it's already declared inside "string.h"

[hotshotennis]

Okay, so should I just delete the whole line? I did, and it seems to compile and run fine, but I'm still not sure if everything is correct or not...

[whiteflags]

The way you declared strlen() is wrong anyway (cause of the error). If you got the prototype correct, it would have been a wasted line, but at least it wouldn't have annoyed the compiler.

size_t strlen (const char *s);

I haven't figured out why people do this sort of thing. Maybe they expect it to work like more modular capabilities in other languages. It doesn't.

[hotshotennis]

The way you declared strlen() is wrong anyway (cause of the error). If you got the prototype correct, it would have been a wasted line, but at least it wouldn't have annoyed the compiler.

size_t strlen (const char *s);

I haven't figured out why people do this sort of thing. Maybe they expect it to work like more modular capabilities in other languages. It doesn't.

- I really don't have any explanation for you. I can tell you that this is not the case for me since C is the first language that I am learning. I honestly don't even remember how I came up with "int strlen(char* strng);". I've been working on this code all day and wrote that particular section a few hours ago. And at this point I'm so tired and dead that I can't think straight. Oh the fun of being a programming newbie. Let's just hope it all eventually clicks.

[nonoob]

When you were told to use strlen, they meant that you should use the 'built in' function. You should not create your own function with the same name. Use strlen16() for example.

int strlen16(char *strng) {
return strlen(strng) == 16; }

... which returns 1 if the string has length 16.