CODEWITHSUNDEEP
c
Maryam
Maryam

Reputation: 63

How to add the first number and last number of a series of number in C?

I am a beginner to C language and also computer programming. I have been trying to solve small problems to build up my skills. Recently, I am trying to solve a problem that says to take input that will decide the number of series it will have, and add the first and last number of a series. My code is not working and I have tried for hours. Can anyone help me solve it?

Here is what I have tried so far. 

#include<stdio.h>

int main()
{
    int a[4];
    int x, y, z, num;
    scanf("%d", &num);
    for (x = 1; x <= num; x++) {
        scanf("%d", &a[x]);

        int add = a[0] + a[4];
        printf("%d\n", a[x]);
    }
    return 0;
}

Upvotes: 2

Views: 914

Answers (2)

Orestis Kapar
Orestis Kapar

Reputation: 128

From from your description it seems clear that you should not care for the numbers in between the first and the last.

Since you want to only add the first and the last you should start by saving the first once you get it from input and then wait for the last number. This means that you don't need an array to save the rest of the numbers since you are not going to use them anyway.

We can make this work even without knowing the length of the series but since it is provided we are going to use it.

#include<stdio.h>

int main()
{
    int first, last, num, x = 0;
    scanf("%d", &num);
    scanf("%d", &first);
    last = first;    //for the case of num=1
    for (x = 1; x < num; x++) {
        scanf("%d", &last);
    }
    int add = first + last;
    printf("%d\n", add);
    return 0;
}

What happens here is that after we read the value from num we immediately scan for the first number. Afterwards, we scan from the remaining num-1 numbers (notice how the for loop runs from 1 to num-1).

In each iteration we overwrite the "last" number we read and when the for loop finishes that last one in the series will actually be the last we read.

So with this input:

4 1 5 5 1

we get output:

2

Some notes: Notice how I have added a last = first after reading the first number. This is because in the case that num is 1 the for loop will never iterate (and even if it did there wouldn't be anything to read). For this reason, in the case that num is 1 it is reasonably assumed that the first number is also the last.

Also, I noticed some misconceptions on your code:

Remember that arrays in C start at 0 and not 1. So an array declared a[4] has positions a[0], a[1], a[2] and a[3]. Accessing a[4], if it works, will result in undefined behavior (eg. adding a number not in the input).

Worth noting (as pointed in a comment), is the fact that you declare your array for size 4 from the start, so you'll end up pretending the input is 4 numbers regardless of what it actually is. This would make sense only if you already knew the input size would be 4. Since you don't, you should declare it after you read the size.

Moreover, some you tried to add the result inside the for loop. That means you tried to add a[0]+a[3] to your result 4 times, 3 before you read a[3] and one after you read it. The correct way here is of course to try the addition after completing the input for loop (as has been pointed out in the comments).

Upvotes: 7

Kienzan
Kienzan

Reputation: 3

I kinda get what you mean, and here is my atttempt at doing the task, according to the requirement. Hope this helps:

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

int main()
{
    int first, last, num, x=0;
    int add=0;
    printf("What is the num value?\n");//num value asked (basically the 
index value)
    scanf("%d", &num);//value for num is stored
    printf("What is the first number?\n");
    scanf("%d", &first);
    if (num==1)
    {
        last=first;
    }
    else
    {
        for (x=1;x<num;x++)
        {
            printf("Enter number %d in the sequence:\n", x);
            scanf("%d", &last);
        }
        add=(first+last);

        printf("Sum of numbers equals:%d\n", add);
    }
    return 0;
}

Upvotes: 0

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