CODEWITHSUNDEEP
carraysaddition
Ali
Ali

Reputation: 27

Addition of two arrays

I tried to add two character arrays or integer arrays. It works correctly only if the values in the array is of one digit. If one or both of the arrays have numbers with two digits I got the wrong answer.

Suppose

//n = 3
a1[n] = "1 2 3"
a2[n] = "4 5 6"

I used while loop to addition ...

while(sizeofarray > i)
{
  result[i]= atoi(&12[i]) + atoi(&a2[i]);
  i++;
}

And i got the correct answer.

But if

a1[n] = "1 10 20"
a2[n] = "4 5 6"

the addition result will be wrong.

What is the correct code to solve this problem. Or at least the idea.

Upvotes: 0

Views: 351

Answers (2)

Damian Yerrick
Damian Yerrick

Reputation: 4664

Each "element" of a C string is a single character, not a "number" in the sense that "10" is one number. For example, these declarations are equivalent:

char a1[] = "1 10 20";
char a1[] = {'1', ' ', '1', '0', ' ', '2', '0', 0};
char a1[] = {49, 32, 49, 48, 32, 50, 32, 0};
/* The 0 at the end is the NUL terminator, which tells the C library
   that the string ends at that point */

If you create a1 and a2 as arrays, you can add corresponding elements.

int a1[] = {1, 10, 20};
int a2[] = {4, 5, 6};

But I'm assuming that you have a need to parse them as strings, and you can't just create arrays directly, such as reading data from standard input (usually the keyboard) or from a file. I see you're using the atoi function to convert a string to a number. But the atoi function does not return how many digits it swallowed up. Thus i++; will skip too few digits unless adding 1-digit numbers. Besides, using one variable (i) to hold the index into both strings works only when the numbers in each string start at the same index, that is, when each element has the same amount of digits.

To fix this, you need to do two things:

  1. Use a separate pointer into each of the a1 and a2 arrays. Each pointer would point to the part of the array that has already been read. This way, after reading two integers from each string, one pointer would point to the end of the "10" and the other to the end of the "5".
  2. Use the strtol function, which returns a pointer to the end of the part of the string that the function has read. You can then use this pointer to skip past the number, and then (manually) skip past whitespace until hitting the next digit (use isdigit) or NUL terminator.

Upvotes: 1

Edwin Buck
Edwin Buck

Reputation: 70979

You have an array of characters, and as such, the digits encoded within the string of characters are not recognized as numbers. This has the side-effect of your program not finding and aligning decimal places during the addition routine.

"10" + "3" would yeild something line "40" if you don't align the decimal places manually. Using arrays of ints would solve the problem as math routines will account for the decimal place alignment automatically for all math types.

To fix this issue, you need to perform a routine

  1. Collect all of the digits for the first number.
  2. Collect all of the digits for the second number.
  3. (assuming that you don't deal with decimal places) perform the addition backwards (from the ones place upwards), carrying if necessary.

Upvotes: 0

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