factorization with loops

Question

factorization with loops

Navigation

#1 by (1 votes)
#2 by (1 votes)

1

I am writing the book 6º edition of C as a program of the Deitel brothers and I am in doubt in an exercise, the exercise is 4.14 of chapter 4 that is about factorization, it asks a program that the user type a number and that number is factored, for example if the user types the number 5, the program will make 5 * 4 * 3 * 2 * 1 resulting in 120. If someone can give me some hint and no answer I will be very grateful thank you:

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

int main()
{
    int i, num, aux1=0, fat=0, aux=0;

    printf("digite um numero para ser fatorado:\n");
    scanf("%i", &num);
    printf("\nvamos fatorar entao o numero %i:\n\n", num);

    for(i=num;i>=1;i--)
    {
        aux=i;
        fat=aux*i;
        printf("%i! ", fat);
    }
    return 0;
}

c

asked by anonymous 02.07.2014 / 20:12

2 answers

1

My tips:

What is the factorial of 0? This would be a better value for initializing fat, since you would print the correct answer if the loop did not run once.

Notice how the final result of fat depends only on the last value of aux , which depends only on the last value of i . I think that's not why you created fat ...

I prefer to iterate from 1 to N instead of N to 1. This makes it easier to write an invariant to the value of fat . If you do not want to think about the invariant then it obviously does)

Tip C:

You can declare deposition variables of any { . It does not have to be all at the top of the function:

{int i; for(i=n; i >= 1; i--){
   int aux = /* ... */
}}

In addition, if you are not using Visual Studio, you can compile your program using the C99 standard that allows you to declare variables in the middle of the

int num;
scanf("%d", &num);

for(int i=n; i >= 1; i--);

02.07.2014 / 20:49

Objective c Basic, error in setNome EXEC_BAD_ACESS How to make a pager without a gridview? [duplicate]

score 1 · Accepted Answer

Notice what you are doing:

Suppose num = 5;

   for(i=num;i>=1;i--)
    {
        aux=i;
        fat=aux*i;
        printf("\n%d ", fat);
    }

Take the bench test:

i=5         |    i=4            |  ...
aux=5       |   aux=4           |
fat=5*5???  |  fat=4*4          |

What you're looking for is this:

i=5         |    i=4            |  ...
aux=5       |   aux=fat   (5)   |
fat=5       |  fat=aux*i (5*4)  |

Note that there are several unnecessary variables and do not forget: 0! = 1 .

Tip: You do not need the aux variable, much less the aux1 you have not even used.