Question

This is my code:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>

int num_mezzo_1(int num_orig);
int num_mezzo_2(int num_orig);

int main(int argc, char *argv[]){
    int num,contatore,tmp=0,tmp_1,tmp_2;
    num=atoi(argv[1]);
    if(num <= 3){
        printf("%d è primo\n", num);
        exit(0);
    }
    else{
        num_mezzo_1(num);
        num_mezzo_2(num);
        tmp=tmp_1+tmp_2;
            //using printf to debug
        printf("t1 %d, t2 %d\n", tmp_1,tmp_2);
        if(tmp>2){
            printf("%d NON è primo\n", num);
        }
        else{
            printf("%d è primo\n", num);
        }
    }
    exit(0);
}

int num_mezzo_1(int num_orig){
    int tmp_1=0,cont_1;
    for(cont_1=1; cont_1<=(num_orig/2); cont_1++){
        if((num_orig % cont_1) == 0){
            tmp_1++;
        }
    }
    //using printf to debug
    printf("\n%d\n", tmp_1);
    return tmp_1;
}

int num_mezzo_2(int num_orig){
    int tmp_2=0,cont_2;
    for(cont_2=((num_orig/2)+1); cont_2<=num_orig; cont_2++){
        if((num_orig % cont_2) == 0){
            tmp_2++;
        }
    }
    //using printf to debug
    printf("\n%d\n\n", tmp_2);
    return tmp_2;
}

This program calculates wheter a number is prime or not.
If i give number 13 as input, the function num_1 has value 1 into tmp_1 and function num_2 has value 1 into tmp_2 and both are correct.
The problem is that tmp=tmp_1+tmp_2 return a big big big value and i don’t understand why.

Answer 1

You are calling the functions num_mezzo_1() and num_mezzo_2() but you are not storing their return values, so your variables tmp_1 and tmp_2 remain uninitialised.

Edit: Try changing the code

    num_mezzo_1(num);
    num_mezzo_2(num);

to

    tmp_1 = num_mezzo_1(num);
    tmp_2 = num_mezzo_2(num);

in the else block and see if you get what you expect.

Working code:

tmp=(num_mezzo_1(num)+num_mezzo_2(num));