Figure 1: Pseudocode to add two BigNums

BigNum add(BigNum a, BigNum b){
  //if |a| > |b| reverse terms
  if(|a|>|b|) return(add(b,a));  
  BigNum sum;      // |a| <= |b|
  carry = 0
  for(i = 0;i<= digits of a; i++){ 
    temp = a[i] + b[i] + carry
    //carry is always 1 or 0
    carry = temp/10
    sum[i] = temp % 10
  }
  for(i=(digits of a) + 1; 
         i<=digits of b; i++){
    //copy the rest of b, and
    //keep track of past carries 
    temp  = b[i] + carry
    carry = temp/10
    sum[i] = temp % 10
  }
  if (carry) sum(i) = carry;
  return sum;
}