1.
#include <stdio.h>
#include<math.h>
typedef struct tocka2D {
 double x;
 double y;
} tocka2D ;

float rastojanie(tocka2D t1, tocka2D t2) {
 return sqrt ((t1.x - t2.x) * (t1.x - t2.x) + (t1.y - t2.y) * (t1.y - t2.y));
}

typedef struct tocka3D {
 double x;
    double y;
    double z;
} tocka3D ;

float rastojanie3D(tocka3D t1, tocka3D t2) {
  return sqrt((t1.x - t2.x) * (t1.x - t2.x) + (t1.y - t2.y) * (t1.y - t2.y)+(t1.z-t2.z)*(t1.z-t2.z));
}

int ista_prava(tocka2D t1, tocka2D t2, tocka2D t3) {
 if((t2.y-t1.y)/(t2.x-t1.x)==(t3.y-t2.y)/(t3.x-t2.x))
      return 1;
    else 
        return 0;
}
int main() {
    float x1, y1, x2, y2;
    scanf("%f %f", &x1;, &y1;);
 scanf("%f %f", &x2;, &y2;);
 tocka2D t1 = { x1, y1 };
 tocka2D t2 = { x2, y2 };
 printf("%.2f\n", rastojanie(t1, t2));
    float z1, z2;
    scanf("%f %f", &z1;, &z2;);
    tocka3D t3 = {x1, y1, z1};
    tocka3D t4 = {x2, y2, z2};
    printf("%.2f\n", rastojanie3D(t3, t4));
    tocka2D t5 = {z1, z2};
    printf("%d\n", ista_prava(t1, t2, t5));
 return 0;
}



2.
 #include <stdio.h>
typedef struct tocka {
    float x;
    float y;
} tocka;
typedef struct otsecka {
    tocka prva;
    tocka vtora;
} otsecka;
 
int se_secat(otsecka o1, otsecka o2) {
        int seSecat = 0;
    float  k1 = (o1.prva.y - o1.vtora.y)/(o1.prva.x - o1.vtora.x);
    float k2 = (o2.prva.y - o2.vtora.y)/(o2.prva.x - o2.vtora.x);
    float b1 = o1.prva.y - k1*o1.prva.x;
    float b2 = o2.vtora.y - k2*o2.vtora.x;
    if(k1 == k2)
    {
        float levaTocka = o1.prva.x;
        float des = o2.vtora.x;
        return levaTocka >= des;
    }
    float finalno_k = k1-k2;
    float finalno_b = b1-b2;
    float res = -finalno_b/finalno_k;
    seSecat = ((res>=o1.prva.x&&res; <= o1.vtora.x)&&(res>= o2.prva.x && res <= o2.vtora.x));
    return seSecat;
}
 
int main() {
    float x1, y1, x2, y2;
    scanf("%f %f %f %f", &x1;, &y1;, &x2;, &y2;);
    tocka t1 = { x1, y1 };
    tocka t2 = { x2, y2 };
    otsecka o1 = { t1, t2 };
    scanf("%f %f %f %f", &x1;, &y1;, &x2;, &y2;);
    t1.x = x1;
    t1.y = y1;
        t2.x = x2;
    t2.y = y2;
     
    otsecka o2 = { t1, t2 };
    printf("%d", se_secat(o1, o2));
    return 0;
}
3.
#include <stdio.h>

typedef struct proizvod
{
    char ime[100];
    int cena;
    int kolicina;
}proizvod ;
int main()
{
    int i,n;
    proizvod p[50];
    scanf("%d", &n);
    for(i=0; i<n; i++)
    {
        scanf("%s",&p[i].ime);
        scanf("%d",&p[i].cena);
        scanf("%d",&p[i].kolicina);
    }
              float vkupno=0;
                  for(i=0; i<n; i++)
              {
                  vkupno+=p[i].kolicina*p[i].cena;
              }
     int b=1;
    for(i=0; i<n; i++)
    {
       
        printf("%d. %s\t%.2f x %d = %.2f\n",b,p[i].ime, (float)p[i].cena,p[i].kolicina, (float)p[i].cena*p[i].kolicina);
        b++;
    }
    printf("Total: %.2f\n",vkupno);
              return 0;
              }