CODEWITHSUNDEEP
cstring
Viva
Viva

Reputation: 2075

How to add two numbers as a string

I have to read from standard input two numbers as strings, in C. How can I print their sum as a string too? I have:

char a[10],b[10];
printf("enter the two numbers");
scanf("%s%s",&a,&b);
char sum[20];
sum=?

A little tip,please? Thank you!

Upvotes: 4

Views: 9460

Answers (5)

Arun
Arun

Reputation: 20383

Unless it is prohibited to do so, then I would approach as the following:

  • Convert the input string(s) to numbers. I would trystrtol().

  • Add the numbers

  • Convert the sum from number to string. I would trysnprintf().

Upvotes: 2

japreiss
japreiss

Reputation: 11251

chars are 8-bit binary numbers, just like smaller ints. We must interpret them to give them meaning as letters.

Your computer probably uses the ASCII standard. In ASCII, the char value representing the character 0 does not actually have the numerical value 0. It's 48. Fortunately, the numbers are all consecutive, so 1 is 49, etc.

char zero = '0';
printf("%d\n", zero);
char one = '1';
printf("%d\n", one);

> 48
> 49

(Note that the %d format flag in printf means "interpret as an integer".)

Since chars are numbers, we can do math with them.

char one = '1';
int one_num = one - '0';
printf("%d\n", one_num);

> 1

Now, you can implement the addition with decimal digits and carrying just like you'd do on paper.

Upvotes: 1

Will Ness
Will Ness

Reputation: 71065

Do this with programming just as you would do it on paper. Make small steps, and make explicit every little step that we do on paper without noticing.

    00111
 ---------
     12345
 123456789
 ---------
 123469134
  • Notice different lengths. You'll need separate vars to hold that info. You'll need to find out the two lengths - either use a standard function, or write your own: strings end with a binary 0.
  • Notice how we go backwards while we add. You'll have to maintain two indices to access the two strings (arrays of chars).
  • Notice how we carry over the high digit of the addition 5+9=14. You'll need to maintain that in another variable.

Use loops. After you've added, you will need to know the total length, and move it to the left edge. Because we don't know in advance what length we'll get, you'll start writing down the answer from the right edge of your sum array. Think, how and what can you improve about this.

Upvotes: 2

pmg
pmg

Reputation: 108968

Just do it like in elementary school

Let's say the input was "...69 + ...63"

9 + 3     = 2 and 1 to go
6 + 6 + 1 = 3 and 1 to go
...

Upvotes: 3

Ameen
Ameen

Reputation: 2586

Convert the strings into numbers using atoi, then add them together, and then print the sum using a print function like printf. See this

Upvotes: 1

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