Program to list prime numbers less than or equal to the input value

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Program to list prime numbers less than or equal to the input value

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Good morning, I want to print a set to which I must print only the primes smaller or equal to the input value, but I cannot succeed, because it always returns the value n and n-1, with the exception of the number 1 (which is not prime). I wonder what’s left for this code to recognize the while and print only the prime numbers.

#include<stdio.h>
int main(){
    int n,res,i,j;
    printf("insira o seu numero aqui\n") 
    scanf("%d",&n);
    printf("Voce inseriu este numero: %d \n",n);
        for (i=n;i>=0;i--){
        res=1;
        j=2;
                    if (i<=1){
                    res=0;
                    while (res==1 && j<=i/2)
                        if (i&j==0)
                        res=0;
                    j++;
                }
                if(res==1)
                printf("%d ",i);
 }
    return 0;
}

I don’t see the point in this test: if (i<=1){. Here: while (res==1 && j<=i/2) if (i&j==0) res=0; can enter infinite loop. The algorithm used does not check whether the number is prime.

– anonimo

2020/10/26 at 17:16
But he didn’t go in, and he didn’t even show up on the print. When I did this algorithm just getting the value by the user to know if it is prime or not it worked. When I tried to add a for and while getting the n-1 of for it n worked. I’m pretty beginner in C. Soon gets this confused.

– TCS

2020/10/26 at 17:45
I was in the logic at: I give the value To each number made the test if it is prime. Who eh cousin he is printed As soon as the test is done he goes down to zero repeats.

– TCS

2020/10/26 at 17:52
Here: if (i&j==0) i don’t know what the result expects to get from this Bitwise AND.

– anonimo

2020/10/26 at 17:58

1 answer

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by anonimo • **4,084** points · Answer 1 · 2020-10-26T17:55:04+00:00

See if this is what you want:

#include<stdio.h>
int main() {
    int n, res, i, j;
    printf("Insira o seu numero aqui: ");
    scanf("%d", &n);
    printf("Voce inseriu este numero: %d \n",n);
    for (i=n; i>1; i--) {
        int j=2;
        while ((j <= i/2) && (i%j != 0))
            j++;
        if (j>i/2)
            printf("%d ",i);
    }
    return 0;
}