I'm making a program that accepts two decimal numbers and convert them into binary numbers, which are stored in integer arrays. Then I need to do multiplication using the two integer arrays. The result should also be a binary integer array (I need to validate that using a for loop). Then I convert them result to decimal number.
So far, I have the following code. My logic to convert the decimal number to binary works fine and vice verse. However, the binary result is always somehow smaller than the expected result. I have spent a lot of time on this, could you help me check what is wrong?
public class BinaryMultiplication {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int num1 = scanner.nextInt();
int num2 = scanner.nextInt();
int[] binaryNum1 = toBinary(num1);
int[] binaryNum2 = toBinary(num2);
System.out.println("Expected result: " + num1 * num2);
System.out.println("Decimal number 1: " + toDecimal(binaryNum1));
System.out.println("Decimal number 2: " + toDecimal(binaryNum2));
int[] resultBinaries = new int[100];
for (int i = 0; i < resultBinaries.length; ++i) {
resultBinaries[i] = 0;
}
for (int i = 0; binaryNum1[i] != -1; ++i) {
for (int j = 0; binaryNum2[j] != -1; ++j) {
resultBinaries[i + j] += binaryNum1[i] * binaryNum2[j] % 2;
resultBinaries[i + j] %= 2;
}
}
resultBinaries[99] = -1;
for (int i = 0; resultBinaries[i] != -1; ++i) {
if (resultBinaries[i] > 1) {
System.out.println("The result is not a binary!!");
}
}
System.out.println("Actual decimal result: " + toDecimal(resultBinaries));
}
public static int toDecimal(int[] binaryNum) {
int result = 0;
int factor = 1;
for (int i = 0; binaryNum[i] != -1; ++i) {
result += binaryNum[i] * factor;
factor *= 2;
}
return result;
}
public static int[] toBinary(int num) {
int[] binaries = new int[100];
int index = 0;
while (num > 0) {
binaries[index++] = num % 2;
num /= 2;
}
binaries[index] = -1;
return binaries;
}
}
A sample input & output: ( the binary validation loop works fine)
45 67
Expected result: 3015
Decimal number 1: 45
Decimal number 2: 67
Actual decimal result: 2871
for (int i = 0; binaryNum1[i] != -1; ++i) {
for (int j = 0; binaryNum2[j] != -1; ++j) {
resultBinaries[i + j] += binaryNum1[i] * binaryNum2[j] % 2;
resultBinaries[i + j] %= 2;
}
}
What happens when resultBinaries[i + j]
increases to 2? It's reduced to 0 and then resultBinaries[i + j + 1]
should be increased with 1, but this isn't happening in the code as far as I can see.
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