C program skipping printf and scanf statements - c

Question

My program below conducts a Caesar's cipher in C. For some reason, after a message has been input by the user, the printf(" \nEnter key:") and
scanf("%d", &key) statements get "jumped" over. My thought was something related to the input buffer having a char and newline entered causing the jump (hence the fflush attempt). How do I prevent this behavior?
#include <stdio.h>
#include <stdlib.h>
int main() {
char message[50], ms;
int i, key, choice;
printf("Enter 1. to Encrypt, or 2. to Decrypt: ");
scanf(" %d", &choice);
printf("Enter a message to process: ");
scanf(" %c", message);
printf(" \nEnter key:");
fflush(stdin);
scanf("%d", &key);
for (i = 0; message[i] != '\0'; ++i) {
ms = message[i];
if (ms >= 'a' && ms <= 'z' && choice == 1) {
ms = ms + key;
if (ms >= 'a' && ms <= 'z' && choice == 2) {
ms = ms - key;
if (ms > 'z') {
ms = ms - 'z' + 'a' - 1;
}
}
message[i] = ms;
} else
if (ms >= 'A' && ms <= 'Z' && choice == 1) {
ms = ms + key;
if (ms >= 'A' && ms <= 'Z' && choice == 2) {
ms = ms - key;
}
if (ms > 'Z') {
ms = ms - 'Z' + 'A' - 1;
}
message[i] = ms;
}
if (choice == 1) {
printf(" \nEncrypted message: %s", message);}
else if (choice == 2) {
printf(" \nDecrypted message: %s", message);}
}
}

Answer 1

#ddisec I have noted 3 mistakes in your code .
First your scanf(" %c", message); .Here you have to use %s (String).
Second the result printing statements should be outside for-loop.
Third putting if(ms >= 'a' && ms <= 'z'&& choice == 2) inside if (ms >= 'a' && ms <= 'z' && choice == 1) dose not make any sense.
Try this corrected code:-
#include <stdio.h>
#include <stdlib.h>
int main()
{
char message[50], ms;
int i, key, choice;
printf("Enter 1. to Encrypt, or 2. to Decrypt: ");
scanf("%d", &choice);
getchar(); // to handle unwanted newline.
printf("Enter a message to process: ");
scanf("%49[^\n]", message);
printf(" \nEnter key:");
scanf("%d", &key);
for (i = 0; message[i] != '\0'; ++i)
{
ms = message[i];
if (ms >= 'a' && ms <= 'z' && choice == 1)
{
ms = ms + key;
}
else if (ms >= 'a' && ms <= 'z' && choice == 2)
{
ms = ms - key;
}
else if (ms > 'z')
{
ms = ms - 'z' + 'a' - 1;
}
else if (ms >= 'A' && ms <= 'Z' && choice == 1)
{
ms = ms + key;
}
else if (ms >= 'A' && ms <= 'Z' && choice == 2)
{
ms = ms - key;
}
else if (ms > 'Z')
{
ms = ms - 'Z' + 'A' - 1;
}
message[i] = ms; // Only single modification code needed.
}
if (choice == 1)
{
printf(" \nEncrypted message: %s", message);
}
else if (choice == 2)
{
printf(" \nDecrypted message: %s", message);
}
}

Answer 2

There are multple problems in your code:
The way you enter the message is incorrect: scanf(" %c", message); reads a single byte into the message first element and does not even make it a C string. Use this instead, to read the message with embedded spaces:
scanf("%49[^\n]", message);
There are logic bugs in the rest of the code: for example, you test for choice == 2 inside the block that is only executed if choice == 1...
Here is a simplified version:
#include <stdio.h>
int main() {
char message[50];
int i, key, choice;
printf("Enter 1. to Encrypt, or 2. to Decrypt: ");
if (scanf("%d", &choice) != 1)
return 1;
printf("\nEnter a message to process: ");
if (scanf("%49[^\n]", message) != 1)
return 1;
printf("\nEnter key:");
if (scanf("%d", &key) != 1)
return 1;
for (i = 0; message[i] != '\0'; ++i) {
int ms = message[i];
if (ms >= 'a' && ms <= 'z') {
if (choice == 1)
ms = 'a' + ((ms - 'a') + key) % 26;
if (choice == 2)
ms = 'a' + ((ms - 'a') + 26 - key) % 26;
message[i] = ms;
} else
if (ms >= 'A' && ms <= 'Z') {
if (choice == 1)
ms = 'A' + ((ms - 'A') + key) % 26;
if (choice == 2)
ms = 'A' + ((ms - 'A') + 26 - key) % 26;
message[i] = ms;
}
}
if (choice == 1)
printf("\nEncrypted message: %s\n", message);
if (choice == 2)
printf("\nDecrypted message: %s\n", message);
}
return 0;
}