Array problem.

**ElJefe05** · 03-29-2017

create a loop of your choice that will subtract the number from itself the number of times equal to the number itself.
for example if i enter a 3 it will do 3-3-3 = -3 or 4 4-4-4-4= -8
thank you for the help in advance

Code:

#include <stdio.h>
 
int main()
{
    int base, exponent, counter, result = 1;
    printf("The number you entered is \n");
    scanf("%d", &base);
     
    for(counter = 0; counter <base; counter++)
    {
        result = result-base;   //  this giving me the wrong number  
    }  
    
    printf("The result is %d" , result);


    return 0;
}

**laserlight** · 03-29-2017

Why do you start with result = 1? It seems to make more sense to start with result = base, though of course you have to do this at the right place. You may also need to adjust the number of iterations of the loop since the number of times you should be subtracting is one less than the base.

**ElJefe05** · 03-29-2017

That's where i 'm confuse on knowing where to start with. Can you explain this to me in better way because i'm new to programing i don't really understand it. Thank you

**laserlight** · 03-29-2017

Let's take the example with 4. You begin the value of 4 (i.e., the initial value of result), then you subtract 4 from that value 3 times. Since you are required to use a loop, that means your loop will loop 3 times.

**ElJefe05** · 03-29-2017

So on line 5 where i'm declaring my variables result should = base

on line 9 for my loop for(counter =0; counter < base; counter++
this is saying the counter is less then the base enter to add one to it correct?
whats the counter = 0 doing ?
and on line 11 that s doing what should take my result and subtract the base (my initial number correct)

**laserlight** · 03-29-2017

Originally Posted by ElJefe05

this is saying the counter is less then the base enter to add one to it correct?
whats the counter = 0 doing ?

Test your program and examine the output. What does the output tell you?

**ElJefe05** · 03-29-2017

Code:

#include <stdio.h>
 
int main()
{
    int base, exponent, counter, result = 0;
    printf("The number you entered is \n");
    scanf("%d", &base);
     
    for(counter = 1; counter <base; counter++)
	{
        result = result-base;   
    }  
    
    printf("The result is %d" , result);


    return 0;
}

for 3 i get -6 and for 4 - 12

**laserlight** · 03-29-2017

Great. Ask yourself why, and keep debugging. It may help to trace through the loop iteration by iteration to see what is happening to the value of result.

**ElJefe05** · 03-29-2017

trust me i've done tried everything and still getting nowhere. I've been at this for like 6hrs i have looked at a few youtube videos but not helping at all. But thank you.

**laserlight** · 03-29-2017

Okay, let's go over your code in post #7 with the input value of 4.

Before the loop:
result = 0; base = 4

The loop begins:
counter = 1; 1 < 4; so counter is incremented to 2 and control enters the loop body.

In the loop body:
result = 0 - 4 = -4

At this point, you should have noticed that something is wrong. You are trying to evaluate 4 - 4 - 4- 4, not 0 - 4 - 4 - 4. So, why do you have 0 - 4?

**ElJefe05** · 03-30-2017

I understand that part now.
ok so start my for(counter = 1; counter <base; counter++)

this means
i start at 1 if enter a 4 its going to check to see the my counter is less than the base if its true then the counter ++ will up the counter by one
so when it does 2 does statment if 2 <4
then 3 < 4
then 4 < 4 then it stops here ,my loop correct
so once it gets to that will print out my result
My question is what is the result = result-base doing is that taking 4-4=0
How to i get it to subtract from itself that's where im lost. If i was going to multiply the number by itself like 4*4*4*4 i would do result = result*base . I've done this already but i don't get why subracting it be anymore different.
T

bY THE WAY thank you for the help.

**laserlight** · 03-30-2017

Originally Posted by ElJefe05

If i was going to multiply the number by itself like 4*4*4*4 i would do result = result*base .

Let's write a version of your program from post #7 to solve this problem that you have proposed:

Code:

#include <stdio.h>

/* This program reads in an integer (assumed to be non-negative) into base and
 * computes base to the power of base */

int main(void)
{
    int base, counter, result = 0;
    printf("The number you entered is \n");
    scanf("%d", &base);

    for (counter = 1; counter < base; counter++)
    {
        result = result * base;
    }

    printf("The result is %d\n", result);

    return 0;
}

Compile and run the above program. Test with a few input values, e.g., 2, 3 and 4. Does it work correctly? Why or why not? If it doesn't work, how would you fix it?

**ElJefe05** · 03-30-2017

no it wont work bc if you set the counter = 1 if counter = 0 will go thru the loop 3times 0 1 2 3x3x3 = 27
it will go counter 1 base 3 ==
counter 2 base 3
result = result*base if i put in 3 is giving me 9 which is wrong b/c its only going thru the loop 2x should be 27

**ElJefe05** · 03-30-2017

for subtraction my result should be result = result - base . Do i need to change my counter++ to counter -- to subtract one less since we are not trying to add them.

**laserlight** · 03-31-2017

Originally Posted by ElJefe05

result = result*base if i put in 3 is giving me 9 which is wrong b/c its only going thru the loop 2x should be 27

Look, I told you to "Compile and run the above program", not write another version of your program, the source which you did not provide, and then tell me what you think is wrong with that unknown program. The program I posted in post #12 utilises the exact same logic as the program that you posted in post #7, except that subtraction was changed to multiplication.

This is important because if you had run and compiled the above program, you would have seen that if you put in 3, you get a result of 0, not 9, not 27. 0. Zero. ZERO.

You get a result of 0 because you are multiplying with 0. As in you are computing 0 * 3 * 3 = 0

Control should only go through the loop twice when the input is 3. You want to compute 3 * 3 * 3, not 3 * 3 * 3 * 3. Likewise, you want to compute 3 - 3 - 3, not 3 - 3 - 3 - 3 (although personally that sounds more like "subtract the number from itself the number of times equal to the number itself"). You can get the correct answer for subtraction by computing 0 - 3, or in the case of 4, 0 - 4 - 4, but that doesn't exactly simulate what your assignment wants you to simulate.

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