The entered values ​are not applied

Question

Why the entered values are not applied? When I used [#include <stdlib.h>] and [rand()], the code was worked. I don't know what is difference.The code is for comparing the sizes of numbers.

#include <stdio.h>

int main(void) {
 int p0, p1, p2, p3;
scanf("%d %d %d %d\n", &p0, &p1, &p2, &p3);
int low1, low2, high1, high2; 
int lowest, middle1, middle2, highest; 
    
if (p0 >= p1) {
        low1 = p1;
        high1 = p0;
    }
    else if (p0 < p1) {
        low1 = p0;
        high1 = p1;
    }
    if (p2 >= p3) {
        low2 = p3;
        high2 = p2;
    }
    else if (p2 < p3) {
        low2 = p3;
        high2 = p3;
    }
    if (low1 <= low2) {
        lowest = low1;
        middle1 = low2;
    }
    else if (low1 > low2) {
        lowest = low2;
        middle1 = low1;
    }
    if (high1 >= high2) {
        highest = high1;
        middle2 = high2;
    }
    else if (high1 < high2) {
        highest = high2;
        middle2 = high1;
    }