C program to multiply large numbers has been shown here. This program follows the standard multiplication algorithm.

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1. Program & Output

## 1. C program & output to Multiply Large numbers

Code has been copied
/************************************
alphabetacoder.com
C program to multiply large numbers
*************************************/

#include <stdio.h>
#include <string.h>
//set maximum size of the input numbers
#define MAX 500

int main() {
// declare varables
char num1[MAX], num2[MAX]; // for storing large numbers.
int result[2 * MAX] = {0};
// for storing the result
int n1, n2, d1, d2, i, j, sum, carry, flag = 0;

printf("Enter the first number: ");
scanf("%s", num1);
printf("Enter the second number: ");
scanf("%s", num2);

//find the number of digits for both numbers.
n1 = strlen(num1);
n2 = strlen(num2);

// Perform multiplication
// Multiply each digit of num1 with each digit of num2
for (i = n1 - 1; i >= 0; i--) {
// initialize
carry = 0;
d1 = num1[i] - '0'; // current digit of first number

for (j = n2 - 1; j >= 0; j--) {
d2 = num2[j] - '0'; // current digit of second number
// calculate sum
sum = d1 * d2 + result[i + j + 1] + carry;
result[i + j + 1] = sum % 10;
// calculate carry
carry = sum / 10;
}

// Set the carry to the leading digit
result[i] = carry;
}

// display the result
printf("Result = ");
for (i = 0; i < (n1 + n2); i++) {
if (result[i])
flag = 1;
if (flag)
printf("%d", result[i]);
}

return 0;
}


Output

Enter the first number: 47771324767464454646465446464688879878974321524857451254875414574512485754124854241578887445787454124857524524545248575454547451248754

Enter the second number: 988754545421215444123485445242415245420445576874135468724578448574657987443994654468745412122124545454878789934557467465465468757786778787878798

Result = 47234114504623567435933878704274485175842876541707331278804882463108053938314071233587846425511881735181565684398142342387514944066523585420570029814418573817692598464892531177169082116019030769201727589777768498535602041076351997994350183545944126849807797118519698443900517692