hillcypher in c code example

Example: hill cipher encryption in c

#include<stdio.h>
#include<math.h>
 
float encrypt[3][1], decrypt[3][1], a[3][3], b[3][3], mes[3][1], c[3][3];
 
void encryption();	//encrypts the message
void decryption();	//decrypts the message
void getKeyMessage();	//gets key and message from user
void inverse();		//finds inverse of key matrix
 
void main() {
	getKeyMessage();
	encryption();
	decryption();
}
 
void encryption() {
	int i, j, k;
	
	for(i = 0; i < 3; i++)
		for(j = 0; j < 1; j++)
			for(k = 0; k < 3; k++)
				encrypt[i][j] = encrypt[i][j] + a[i][k] * mes[k][j];
	
	printf("\nEncrypted string is: ");
	for(i = 0; i < 3; i++)
		printf("%c", (char)(fmod(encrypt[i][0], 26) + 97));
 
}
 
void decryption() {
	int i, j, k;
	
	inverse();
	
	for(i = 0; i < 3; i++)
		for(j = 0; j < 1; j++)
			for(k = 0; k < 3; k++)
				decrypt[i][j] = decrypt[i][j] + b[i][k] * encrypt[k][j];
	
	printf("\nDecrypted string is: ");
	for(i = 0; i < 3; i++)
		printf("%c", (char)(fmod(decrypt[i][0], 26) + 97));
	
	printf("\n");
}
 
void getKeyMessage() {
	int i, j;
	char msg[3];
 
	printf("Enter 3x3 matrix for key (It should be inversible):\n");
	
	for(i = 0; i < 3; i++)
		for(j = 0; j < 3; j++) {
			scanf("%f", &a[i][j]);
			c[i][j] = a[i][j];
		}
	
	printf("\nEnter a 3 letter string: ");
	scanf("%s", msg);
	
	for(i = 0; i < 3; i++)
		mes[i][0] = msg[i] - 97;
}
 
void inverse() {
	int i, j, k;
	float p, q;
	
	for(i = 0; i < 3; i++)
		for(j = 0; j < 3; j++) {
			if(i == j)
				b[i][j]=1;
			else
				b[i][j]=0;
		}
		
	for(k = 0; k < 3; k++) {
		for(i = 0; i < 3; i++) {
			p = c[i][k];
			q = c[k][k];
				
			for(j = 0; j < 3; j++) {
				if(i != k) {
					c[i][j] = c[i][j]*q - p*c[k][j];
					b[i][j] = b[i][j]*q - p*b[k][j];
				}
			}
		}
	}
	
	for(i = 0; i < 3; i++)
		for(j = 0; j < 3; j++)
			b[i][j] = b[i][j] / c[i][i];
	
	printf("\n\nInverse Matrix is:\n");
	for(i = 0; i < 3; i++) {
		for(j = 0; j < 3; j++)
			printf("%d ", b[i][j]);
		
		printf("\n");
	}
}