Value from one void function to another using pointers?

Question

I've looked around but can't seem to find how to do this. I want the value of empty lines from test2(int *f) to be passed to test1() and be printed on the screen.

Variant 1 of code:

#include <stdio.h>
#include <string.h>
void test1();
void test2(int *f);
void test1(){
    int a;
    test2(&a);
    printf("%d \n", a);
}
void test2(int *f){
    char str[80];
    int lines, i,  emptylines=0;
    *f=emptylines;
    printf("Type a program here. Ctrl+Z and enter to stop.\n");
    fflush(stdin);
    while(gets(str)!=NULL && strcmp(str, "qq")) {
        for(i=0; i<strlen(str); i++){
            if(str[i]!='\n') lines=1;
        }
        if(!lines) emptylines++;
            lines=0;
    }
}
int main() {
    test1();
    return 0;
}

Variant 2 of code:

#include <stdio.h>
#include <string.h>
void test1();
void test2(int *f);
void test1(){
    int a;
    test2(&a);
    printf("%d \n", a);
}
void test2(int *f){
    char str[80], *p;
    int lines, emptylines=0;
    *f=emptylines;
    printf("Type a program here. Ctrl+Z and enter to stop.\n");
    fflush(stdin);
    while(gets(str)!=NULL && strcmp(str, "qq")) {
        p=str;
        lines=0;
        while(*p!='\0') {
            if(*p!=' ') {
                lines=1;
            }
            p++;
        }
        if(lines==0){
            emptylines++;
            lines=0;
        }
    }
}
int main() {
    test1();
    return 0;
}

Answer 1

You are putting *f=emptylines in the beginning of the function void test2(int *f); Then you calculate emptylines but this will not affect the value pointed-to by f.

You need to move that assignment *f=emptylines to the end of the function, just before returning and after having calculated emptylines

void test2(int *f){
    // stuff to calculate emptylines
    ....

    *f=emptylines; // at the end
}

Answer 2

When you write

*f = emptylines;

you are copying the value of emptylines into the space pointed to by f. Then when you update emptylines later, the value pointed to by f doesn't change because you made a copy.