#include <stdio.h>
#include <string.h>
#include <ctype.h>
// Correct Verhoeff multiplication table
int d[10][10] = {
{0,1,2,3,4,5,6,7,8,9},
{1,2,3,4,0,6,7,8,9,5},
{2,3,4,0,1,7,8,9,5,6},
{3,4,0,1,2,8,9,5,6,7},
{4,0,1,2,3,9,5,6,7,8},
{5,9,8,7,6,0,4,3,2,1},
{6,5,9,8,7,1,0,4,3,2},
{7,6,5,9,8,2,1,0,4,3},
{8,7,6,5,9,3,2,1,0,4},
{9,8,7,6,5,4,3,2,1,0}
};
// Permutation table
int p[8][10] = {
{0,1,2,3,4,5,6,7,8,9},
{1,5,7,6,2,8,3,0,9,4},
{5,8,0,3,7,9,6,1,4,2},
{8,9,1,6,0,4,3,5,2,7},
{9,4,5,3,1,2,6,8,7,0},
{4,2,8,6,5,7,3,9,0,1},
{2,7,9,3,8,0,6,4,1,5},
{7,0,4,6,9,1,3,2,5,8}
};
// Inverse table
int inv[10] = {0,4,3,2,1,5,6,7,8,9};
// Generate checksum (last digit)
int generateChecksum(char num[]) {
int c = 0;
int len = strlen(num);
for(int i = len - 1, pos = 0; i >= 0; i--, pos++) {
c = d[c][ p[(pos + 1) % 8][ num[i] - '0' ] ];
}
return inv[c];
}
int main() {
char input[20];
printf("Enter first 11 digits of Aadhaar: ");
scanf("%s", input);
if(strlen(input) != 11) {
printf("Input must be exactly 11 digits!\n");
return 0;
}
for(int i = 0; i < 11; i++) {
if(!isdigit(input[i])) {
printf("Invalid! Only digits allowed.\n");
return 0;
}
}
int lastDigit = generateChecksum(input);
printf("\nPredicted Checksum (Last Digit) = %d\n", lastDigit);
printf("Predicted Valid Aadhaar Number = %s%d\n", input, lastDigit);
return 0;
}
