Very simple C Function

How do I use the following function?

/* sets the variable referenced by r to zero and returns the previous value of r */
int testfunc(int *r);

Code (markup):

I'm trying the following but no luck?

#include <stdio.h>
#include "testfunc.h"

int main()
{
        int testValue=1;
        int testResult;

        testfunc(testValue);

        printf("Test value now equals %d\n",testValue);
        printf("Returned value equals %d\n",testResult);

        return 0;
}

Code (markup):

 

Hi,

try this:

int main(){
        int testResult,testValue=1;
testResult = testfunc(&testValue);
printf("Test value now equals %d\nReturned value equals %d\n",testValue,testResult);
return 0;
}

PHP:

 

What does the:

int *r

Code (markup):

Acutally mean? I've not come across the * before.

 

This is pointer - check this link

 

I'm receiving the following error when compiling:

gcc testlscore.c -o testscore
/tmp/ccQRp93p.o: In function `main':
/tmp/ccQRp93p.o(.text+0x26): undefined reference to `testfunc'
collect2: ld returned 1 exit status

Code (markup):

 

It seems you forgot to include the file with testfunc().

testfunc.h holds only function prototype definition (I guess), not the function itself: testfunc.c or testfunc.cpp?
Here is my test and it works under Xubuntu:

#include <stdio.h>

int testfunc(int *r);
int main(void){
        int testResult,testValue=1;
testResult = testfunc(&testValue);
printf("Test value now equals %d\nReturned value equals %d\n",testValue,testResult);
return 0;
}
int testfunc(int *r){
int tmp;
tmp=*r;
*r=0;
return tmp;
}

PHP: