public String multiply(String one, String two) { char[] one_char; char[] two_char; int carry = 0; if(one.length() > two.length()){ one_char = one.toCharArray(); two_char = two.toCharArray(); } else{ one_char = two.toCharArray(); two_char = one.toCharArray(); } int[] result = new int[one_char.length + two_char.length]; for(int index = two_char.length - 1; index >= 0 ;index--){ for(int index2 = one_char.length - 1; index2 >= 0 ;index2--){ int value = ((one_char[index2] - '0') * (two_char[index] - '0')) + result[(index2 + index) + 1]; result[(index2 + index) + 1] = value % 10; carry = value / 10; result[(index2 + index)] += carry; } } return Arrays.toString(result); }

public static void main(String[] args) { String s1 = "4567"; String s2 = "1234"; int res = convertString2Int(s1) * convertString2Int(s2); System.out.println(res); } public static int convertString2Int(String s){ char []chs = s.toCharArray(); int n1 = 0; for(int i=0; i < chs.length ; i++){ n1 = n1 + (chs[i]-'0') * getPowerOf(10, chs.length-i); } return n1; } public static int getPowerOf(int num, int times){ int val = 1; for(int i =0; i

//Assumption +ve interger ... no sigh, no .,no float resut is within range of int int multiplicationWithoutCast(string str1,string str2) { int finalresult=0; if(str2.length() == 1) { int result=0; int intResult =0; int carry = 0; int j = 1; // used unsigned int i so infinite loop bcz never goes below zero for(int i=str1.length()-1; i>=0; i--,j=j*10) // u did j+10 first :/ { intResult = (str1[i] - '0' ) * (str2[0] -'0') + carry; //cout =0;i--,j=j*10) { finalresult = finalresult + multiplicationWithoutCast(str1,str2.substr(i,1)) * j; } return finalresult; } }

I tried many methods but was not successful or/and efficient

How about getting the ascii code for each character, substracting 48, then you would have each digit. Then you can multiply them?

1. Add using a loop. Or 2. Bitwise operation.

// C# static int StrToInt( string s ) { if( s == null ) return int.MinValue; int n = 0; for( int i = s.Length - 1; i >= 0; --i ) n = (n * 10) + (s[i] - '0'); return n; } static int MultiplyStrings( string s1, string s2 ) { int n1 = StrToInt( s1 ); int n2 = StrToInt( s2 ); return n1 * n2 ; }