large number multi plication

hi all i am trying to multiply to big numbers..the code is here as u scroll down to the last part i am unable to get the result for multiplication ..can some one help me out please the addition is successful





#include <stdio.h>
#include <stdlib.h>
#include<iostream>
#include<ncurses.h>
#include<string.h>

using namespace std;

int main ()
{
int i=0,k=0;
int tmp1=0, tmp2=0, tmp3=0;
char * a;
a= (char *) malloc(30 * sizeof(char));

char * b;
b= (char *) malloc(30 * sizeof(char));

int * x;
x= (int *) malloc(30 * sizeof(int));

int * y;
y= (int *) malloc(30 * sizeof(int));

int * z;
z= (int *) malloc(61 * sizeof(int));

int * w;
w= (int *) malloc(31 * sizeof(int));

int * v;
v= (int *) malloc(61 * sizeof(int));

int * solution;
solution= (int *) malloc(61 * sizeof(int));


int carry = 0;
int c[61];
int d[61];

int f[61];
int g[61];

cout<<"\nEnter a number (up to 30 digits in length)> "; cin >> a;

i=0;

while(i < strlen(a)){
c[i] = a[i] - '0';
i++;}


cout << "\nThe first number is: ";

for(i=0; i < strlen(a); i++){
cout << c[i];}

cout <<"\n";


//string reversal

for(i=0, k = 29; i < strlen(a); i++){
x[k] = c[(strlen(a)-1)-i];
k--;}

cout << "\nEnter a second number (up to 30 digits in length)> "; cin >> b;

i=0;
while(i < strlen(b)){
d[i] = b[i] - '0';
i++;}

cout << "\nThe second number is: ";

for(i=0; i < strlen(b); i++){
cout << d[i];}
cout << "\n";

//string reversal

for(i=0, k = 29; i < strlen(b); i++){
y[k] = d[(strlen(b)-1)-i];
cout <<"\nThe sum of the two numbers is: ";

for(k=30; k>=0; k--)
{
w[k] = 0; //w[k] initialised
}

//addition

for (k = 29; k >= 0; k--){
w[k] = x[k] + y[k] + w[k]; //+w[k] is accounting for the carry

//carry taken care of

if (w[k] >= 10){
w[k] = w[k]%10;
w[k-1] = 1;}
}

for(i= -1; i < 30; i++){
cout << w[i];}

cout <<"\n";

for(k = 60; k>=0; k--){
z[k] = 0;
f[k] = 0;
g[k] = 0;
solution[k] = 0;
}
for(k = 0; k < 30; k++){
f[k+31] = x[k];
g[k+31] = y[k];
}

cout <<"\nThe product of the two numbers is: ";

/*The multiplication algorithm begins here*/

for(i= 60; i >= 0; i--) {
for(k=60; k>=0; k--)
{ tmp1 = f[i] * g[k];
z[k] = tmp3 + z[k-1];
tmp3 = tmp1 % 10;
z[k-1]= tmp1 / 10;
}
}

/*The multiplication algorithm ends here*/

for(i = 0; i < 61; i++){
cout << z[i];}
cout <<"\n\n";

return 0;
}
}

1) Please use code tags when posting code. The code you posted is unreadable due it being unformatted.

2) Why are you using malloc()? Why not just declare arrays?

3) Your program has memory leaks due to never calling free().

4) Use more descriptive names for your variables instead of "x", "y", "z", etc.

5) You should break down that entire main() function into more functions. There should be a function just to add to big numbers, a function to reverse numbers, etc. Making one huge main() function gets confusing and unwieldly.

6) Did you use a debugger? If not, please do so to know exactly what your program is doing at each step.

Regards,

Paul McKenzie

Besides what Paul already pointed out, it's not clear what the issue is. You may want to try using 64-bit types instead of 32-bit ones, and by that I mean __int64 instead of int, that may help if your value wraps around 2+ billion for int.

Quote:

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Originally Posted by Paul McKenzie

1) Please use code tags when posting code.

---

Paul, I'm not sure if you have access to the webmaster of this site, but it would greatly help if they installed a "code" button, like many forums now have, that will insert the code block automatically.

They do. It's the small button with the word 'Code' written on it. :thumb:

Quote:

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Originally Posted by ankscorek

hi all i am trying to multiply to big numbers..

---

Are you attempting to write this in C or C++?
Nearly all of your code is in C, except for the <iostream> functions.

It should be worth pointing out, assuming you want to learn a lot more about C++, that experienced C++ coders, if asked to do this task from scratch, would most probably create a Big_Number class with overloaded arithmetic and streaming operators.

i.e.

Code:

---

Big_Number a;
Big_Number b;

cout <<  "Enter the first number";
cin >> a;

cout <<  "Enter the second number";
cin >> b;

Big_Number c = a + b;

cout << "The sum is " << c;

---

This is probably way beyond your understanding of C++ at the moment, but should show you what can be achieved.

Quote:

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Originally Posted by JohnW@Wessex

They do. It's the small button with the word 'Code' written on it. :thumb:

---

I'm not sure what browser you use, my Firefox doesn't have such button. Take a look.... :thumb:

Hi,

To see the "code" and all the other nice buttons go to the User CP -> Edit Options -> Miscelaneous Options -> Editor Interface.

With regards
Programartist

Quote:

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Originally Posted by ProgramArtist

To see the "code" and all the other nice buttons go to the User CP -> Edit Options -> Miscelaneous Options -> Editor Interface.

---

You see, this all should be available by default... I've been using this forum for all this time and had no clue that it was there :) What would you expect from a novice user then?

Quote:

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Originally Posted by dc_2000

You see, this all should be available by default...

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Strange, since I've never had to set anything to see the code tags button.

Regards,

Paul McKenzie

Quote:

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Originally Posted by Paul McKenzie

Strange, since I've never had to set anything to see the code tags button.

---

There likely was a change in editor interface (e.g., when updating vbulletin) that your forum participation pre-dated.