Create Luhn_Algorithm.c

Author: silven-mohan

Luhn_Algorithm.c

@@ -0,0 +1,48 @@
+int Luhn_Algorithm()
+{
+	int i, k, digit, value=0, f=0, len;
+	char num[20];
+	printf("Enter the number:");
+	scanf("%s", &num);
+	len=strlen(num);
+	// Length Check
+	if(len!=16)
+	{
+		printf("Enter a valid 16-digit number.");
+		return 0;
+	}
+	// Check for Invalid Characters
+	for(i=0;i<=(len-1);i++)
+	{
+		if((isdigit(num[i]))==0)
+		{
+			printf("Invalid Character %c. Enter a valid 16-digit number only.", num[i]);
+			return 0;
+		}
+	}
+	// Main Logic
+	for(i=0;i<=14;i=i+2)
+	{
+		digit=(num[i]-'0');
+		k=digit*2;
+		if(k>9)
+		{
+			k=k-9;
+		}
+		value=value+k;
+	}
+	for(i=1;i<=15;i=i+2)
+	{
+		digit=(num[i]-'0');
+		value=value+digit;
+	}
+	if((value%10)==0)
+	{
+		printf("%s passes Luhn's Algorithm'.", num);
+	}
+	else
+	{
+		printf("%s does not pass Luhn's Algorithm'.", num);
+	}
+	return 0;
+}