C++: Will Not Accept New C-String Input - c++

Question

First off, thanks in advance for your help. This issue is driving me nuts.
I have a program that accepts a c-string, and then can count the number of vowels and consonants. This works without issue. However, I also need to include a function that allows the user to create a new string. The problem is, though, when the user selects "new string" from the menu, it just loops through the newString() method, without waiting for the user's input. It then creates a new, blank screen.
Here is the entire program. The newString() method is at the end.
#include <iostream>
using namespace std;
// function prototype
void printmenu(void);
int vowelCount(char *);
int consCount(char *);
int cons_and_vowelCount(char *);
void newString(char *, const int);
int main() {
const int LENGTH = 101;
char input_string[LENGTH]; //user defined string
char choice; //user menu choice
bool not_done = true; //loop control flag
// create the input_string object
cout << "Enter a string of no more than " << LENGTH-1 << " characters:\n";
cin.getline(input_string, LENGTH);
do {
printmenu();
cin >> choice;
switch(choice)
{
case 'a':
case 'A':
vowelCount(input_string);
break;
case 'b':
case 'B':
consCount(input_string);
break;
case 'c':
case 'C':
cons_and_vowelCount(input_string);
break;
case 'd':
case 'D':
newString(input_string, LENGTH);
break;
case 'e':
case 'E':
exit(0);
default:
cout << endl << "Error: '" << choice << "' is an invalid selection" << endl;
break;
} //close switch
} //close do
while (not_done);
return 0;
} // close main
/* Function printmenu()
* Input:
* none
* Process:
* Prints the menu of query choices
* Output:
* Prints the menu of query choices
*/
void printmenu(void)
{
cout << endl << endl;
cout << "A) Count the number of vowels in the string" << endl;
cout << "B) Count the number of consonants in the string" << endl;
cout << "C) Count both the vowels and consonants in the string" << endl;
cout << "D) Enter another string" << endl;
cout << "E) Exit the program" << endl;
cout << endl << "Enter your selection: ";
return;
}
int vowelCount(char *str) {
char vowels[11] = "aeiouAEIOU";
int vowel_count = 0;
for (int i = 0; i < strlen(str); i++) {
for (int j = 0; j < strlen(vowels); j++) {
if (str[i] == vowels[j]) {
vowel_count++;
}
}
}
cout << "String contains " << vowel_count << " vowels" << endl;
return vowel_count;
} // close vowelCount
int consCount(char *str) {
char cons[43] = "bcdfghjklmnpqrstvwxyzBCDFGHJKLMNPQRSTVWXYZ";
int cons_count = 0;
for (int i = 0; i < strlen(str); i ++) {
for (int j = 0; j < strlen(cons); j++) {
if (str[i] == cons[j]) {
cons_count++;
}
}
}
cout << "String contains " << cons_count << " consonants" << endl;
return cons_count;
} // close consCount
int cons_and_vowelCount(char *str) {
int cons = consCount(str);
int vowels = vowelCount(str);
int total = cons + vowels;
cout << "The string contains a total of " << total << " vowels and "
"consonants" << endl;
return total;
}
void newString(char *str, int len) {
cout << "Enter a string of no more than " << len-1 << " characters:\n";
cin.getline(str, len);
return;
}

Answer 1

The statement cin >> choice only consumes the character they type, not the carriage return that follows. Thus, the subsequent getline() call reads an empty line. One simple solution is to call getline() instead of cin >> choice and then use the first character as the choice.
BTW, the while (not done) should immediately follow the do { … }, and the return 0 is redundant. Also, you should call newString at the start of the program instead of repeating its contents.

Answer 2

cin >> choice leaves a newline in the input stream.. which cause the next getline() to consume it and return. There are many ways.. one way is to use cin.ignore() right after cin >> choice.

Answer 3

The cin >> choice only consumes one character from the stream (as already mentioned). You should add
cin.ignore(std::numeric_limits<std::streamsize>::max(),'\n');
right after cin>>choice to ignore all the characters that come into the stream after reading the choice.
p.s. #include <limits>