Question

Recently in an interview i was asked a question to write a function which takes two character arrays(integers) as input and returns the output character array.

Function Signature:

char* find_sum(char* a, char* b)

How would one approach this?

Example scenario:

find_sum("12345","32142") = "44487"

Note:

The number of digits can be many(1-100).

Answer 1

u can add huge numbers using the char array approach. however you need to delete the char* after using it every time or use some smart pointer.

 char* find_sum(char* a, char* b) {
    int lenA = strlen(a), lenB = strlen(b);
    int max = lenA > lenB ? lenA : lenB; // Get the max for allocation
    char* res = (char*)malloc (max+2);
    memset(res, '0', max +1);      // set the result to all zeros
    res[max+1] = '\0';
    int i=lenA - 1, j = lenB - 1, k = max;
    for (; i >= 0 || j >=0; --i, --j, --k) {
            int sum = 0;
            if (i >= 0 && j>=0)
                    sum = a[i] - '0' + b[j] - '0' + res[k] - '0' ;  // add using carry
            else if (j >= 0)
                    sum =  b[j] - '0' + res[k] - '0' ;     // add the carry with remaining
            else if (i >= 0)
                    sum =  a[i] - '0' + res[k] - '0' ;
            res[k] = sum % 10 + '0';
            res[k-1] = sum / 10 + '0';
    }
    return res;
 }

 int main() {
    printf (" sum = %s ", find_sum("12345432409240242342342342234234234", "9934563424242424242423442424234"));
    return 0;
 }

Note: The precondition for the function is the input char arrays should contain only numbers.