C中的无限While循环

Question

this code is creating me an infinite loop i want to follow some steps getting the number debut to 0 adn printing how much steps it tooks the program to do it

    int debut,i;
    printf("de (>= 1) ? ");
    do
    {            
        scanf("%d",&debut);
    } 
    while (debut < 1);

    int fin;
    printf("a >=  <<  << ) ? ");
    do 
    {            
        scanf("%d",&fin) ;
    } 
    while (fin < debut);

   for (;debut<=fin;debut++){
       i=0;
       while(debut!=0)
       {
           if(debut%3==0)
           {
               debut+=4;
           }
           else if (debut%3!=0 && debut%4==0){
               debut/=2;
           }
           else if (debut%3!=0 && debut%4!=0)
           {
               debut-=1;
           }
           i+=1;

       }
       printf("%d\n->%d",debut,i);    
       }

Answer 1

for(debut<=fin;debut++) {
    while(debut!=0) {
        //do stuff
    }
    //debut == 0, debut <= fin
}

Okay, massive edit to my answer. I was looking at the wrong loop.

In order to enter the for loop, debut must be <=fin . Any time that fin is >0 , and the for loop is entered, you'll be stuck in the for loop.

You're stuck in the while loop until debut == 0 returns true . As long as debut++ <= fin , you're stuck in the for loop. You're modifying debut in the while loop, but fin remains the same value. So the while loop reduces debut to 0 and the for loop goes to the next iteration every time.

Answer 2

Short Answer : I suspect that you intended your while loop to work on a copy of debut , and not debut itself.

---

• Let's assume that debut == 3 and fin == 5 .
• We execute the first iteration of the for loop, which involves a complete walkthrough of the while loop.
• After the while loop, we have debut == 0 , fin == 5 , and i == 12 .
• We then print some information.
• However, we are now going to iterate on the for loop again. debut has been decreased to 0 , because of the work we did, and so each time we run through this code, at the end of the for loop iteration, we are going to have a debut == 0 , which will cause the for loop to never exit.

---

It may be more helpful to show this inline with the code...

for (;debut<=fin;debut++){
    // Let's assume we get here. We can assume some sane debut and fin values,
    // such as the 3 and 5 suggested above.

    int i=0;
    while (debut != 0) {
        // Stuff happens that makes debut go to zero.
    }

    // To get to this point, we __know__ that debut == 0.
    // We know this because that's the condition in the while loop.

    // Therefore, when we do the comparison in the for loop above for the
    // next iteration, it will succeed over and over again, because debut
    // has been changed to zero.

    printf("%d->%d\n",debut,i);
}

---

Personally, I suspect you're looking for the number of iterations for a set of numbers. This to me sounds like a perfect place to use a function. The code I would suggest would look something like this.

#include <stdio.h>

int iterations(int debut) {
    int i = 0;

    while(debut!=0)
    {
        if(debut%3==0)
        {
            debut+=4;
        }
        else if (debut%3!=0 && debut%4==0){
            debut/=2;
        }
        else if (debut%3!=0 && debut%4!=0)
        {
            debut-=1;
        }

        i+=1;
    }

    return i;
}

int main() {
    int debut = 3;
    int fin = 5;

    for (;debut<=fin;debut++) {
        printf("%d -> %d\n", debut, iterations(debut));
    }
}

---

Also, just for the sake of noting things, please note that in the example code that I've given at the end, I removed all of the input scanf code. It's not related to your actual problem, and it reduces the total amount of code that anyone needs to scan to understand where your problem is.