I have a little problem with entering characters in C language. The program works fine after the first iteration of the loop, all the options from the MENU a), b), c), d), e) work. The problem, however, appears in subsequent iterations of the loop with the "a" and "c" options. It is as if it does not load characters immediately, only in the following lines. I put a link with an overview screen with the code and the console window.
Or maybe the problem is in another piece of code?
That's my fragment of code:
char menu(void) {
int ch;
printf("Enter the letter corresponding to the selected option:\n");
printf(" a) adding numbers to the BST tree from the keyboard \n");
printf(" b) adding random numbers to the tree to determine the number of numbers \n");
printf(" c) writing numbers in order from the smallest \n");
printf(" d) removing a specific number \n");
printf(" e) end \n");
while ((ch = getchar()) != EOF)
{
while (getchar() != '\n')
{
continue;
}
ch = tolower(ch);
if (strchr("abcde", ch) == NULL)
puts("Enter a, b, c, d or e:");
else
break;
}
if (ch == EOF)
ch = 'e';
return ch;
}
int main(int argc, char* argv[]) //This is main function
{
int number, size, size_moose, element_to_delete;
int left_compartment, right_compartment;
char choice;
root = NULL;
printf("Welcome to a number sorting program that uses the BST (Binary Search Tree) sorting algorithm\n");
printf("####################################################################################################\n");
printf("####################################################################################################\n");
printf("\t\tMENU\n\n");
while ((choice = menu()) != 'e') {
switch (choice) {
case 'a':
printf("How many numbers do you want to enter?\n");
scanf("%d", &size);
printf("Enter the numbers one after the other:\n");
for (int i = 0; i < size; i++)
{
scanf("%d", &number);
dodawanie(number, root); //the name of the adding function
}
printf("\n");
break;
case 'b':
printf("How many numbers do you want to draw?\n");
scanf("%d", &size_moose);
printf("Enter the left boundary of the range (e.g. 1):\n");
scanf("%d", &left_compartment);
printf("Enter the right bound of the range (e.g. 100):\n");
scanf("%d", &right_compartment);
for (int i = 0; i < size_moose; i++)
{
//using a random number function
number = losowanie(left_compartment, right_compartment);
dodawanie(number, root);
}
printf("...I drew a %d number/numbers...\n", size_moose);
printf("\n");
break;
case 'c':
printf("Listing the numbers in order from the smallest:\n");
in_order_tree_walk(root); //a function that prints out ordered numbers
printf("\n");
break;
case 'd':
printf("Give a specific value to delete:\n");
scanf("%d", &element_to_delete);
kasowanie(szukaj(root, element_to_delete)); //using a function to remove a specific element
printf("\n");
break;
default:
printf("Error in switch statement\n");
}
}
printf("####################################################################################################\n");
printf("####################################################################################################\n");
printf("Goodbye!\n");
return 0;
}
I put a screen with an example of the program's operation
problemC
Related
I am trying to create a program that assigns the user one of three questions at random. I figured out that part however I want to make it so that after they correctly answer their assigned question that they are asked if they want to take another one.
int main(void) {
srand(time(0));
int luckyNumber;
int quizNumber;
int score;
int totalScore;
int averageScore;
int attempts;
char answer1;
char answer2;
char answer3;
char opt1;
char loop = 'y';
printf("Welcome to the quiz program!\n");
while(loop == 'y') {
printf("Please enter a lucky number between 1 and 9: ");
scanf("%d", &luckyNumber);
quizNumber = rand() % 3 + 1;
printf("Your quiz number is %d\n", quizNumber);
if (quizNumber == quizNumber) {
while (score != 5) {
printf("Quiz 1\n");
printf("A. True\n");
printf("B. False\n");
printf("Enter your answer: ");
scanf(" %c", &answer1);
if (answer1 == 'B' || answer1 == 'b') {
printf("Correct!\n");
score = score + 5;
break;
}
else {
printf("Incorrect!, Try again.\n");
printf("\n");
}
break;
}
break;
}
printf("Would you like to go again y/n?");
scanf("%c", &loop);
if (loop != 'y')
loop = 'n';
}
return 0;
}
The problem I am having is after I compile the code, it stops when the correct answer is input rather than going on to ask if the user would like to do another quiz.
All the cases work except the switch 'a' case. The a case runs the insert method below. Any help would be appreciated, thanks. printf statements inside the switch statement don't work.
void insert() {
char name;
printf("enter your name");
scanf("%c", &name);
for(int i = 0; i < LENGTH; i++){
if (!Thesame(names[1], name) == 0 && counter != LENGTH && strlen(name) <= MAX){
for(int j = 0; j < LENGTH; j++){
strcpy(names[counter],name);
}
}
else{
printf("error");
}
}
```
int main() {
while (1) {
char input;
printf("Type in 'a' be added to the system \n");
printf("Type in 'n' to print next patient and remove from
waitlist \n");
printf("Type in 'l' to list the patients on the waitlist \n");
printf("Type in 'q' to quit the program \n");
scanf("%c", &input);
switch (input) {
case 'a':
insert();
break;
case 'n':
next();
break;
case 'l':
print();
break;
case 'q':
return 0;
}
}
}
char name;: name can contain only a single character. So when you type for example: cuq, name will contain c, then insert does whatever with name and then returns to main. Then in main scanf("%c", &input) will read the remaining characters from the input buffer ('u' and 'q') and because of case 'q': the programs stops. Use a debugger or put some printfs at strategic places in your code to see what happens.
You want a string here and you probably want something like this in insert:
char name[100];
printf("enter your name: ");
scanf("%s", name);
...
You also probably need to change the Thesame function.
I am a beginner in C programming and I am stuck in my little program .
I just wanna make a list from which I ask users to select a number from that list. Then the program should do what it should be done.
My list is:
Create a table
Max & Min Number Checking
Negative & Positive Number Checking
Ascending Order
Descending order
Exit
I couldn't start correctly! When I first press 1 to create the table, the program keeps looping again and again!!
I want my program to ask me for some values then take my value and draw me a table and then store these values temporary in memory, so that I can execute the rest of commands from my list.
Here's my code:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int t[100],n,a,f,s=0,i,max,min,m,l;
{
printf("Welcome to My simple Math Program in C language \n");
printf("1:Create a table\n 2:Max&Min Number Checking\n 3:Negative&Positive Number Checking\n 4:Ascending Order\n 5:Descending ordert\n 6:Exit\n ");
printf("Please Choose a number from the list" );
scanf("%d",&a);
while(a!=6){
switch(a){
case 1:printf("Please Enter The Length Of Your Table ");
scanf("%d",&n);
printf("Please Enter Your Table Elements ");
for(int i=0;i<n;i++){
scanf("%d",&t[i]);
}
for(int i=0;i<n;i++){
printf("%d ",t[i]);
}
break;
case 3:
if(t[i]<0){
printf("This Number is Negative %d",t[i]);
}
else if(t[i]==0){
printf("This Number is nulle %d",t[i]);
}
else
{
printf("This Number is Positive %d",t[i]);
}
;break;
case 6:
break;
}
}
return 0;
}
}
Your scanf() statement is outside your while loop so it is only executed once. You need something like this:
do
{
scanf("%d",&a);
...rest of code
} while (a!=6)
You should print the message and read the option inside the main loop:
#include <stdio.h>
#include <stdlib.h>
int main() {
int t[100], n, a, f, s = 0, i, max, min, m, l;
printf("Welcome to My simple Math Program in C language\n");
for (;;) {
printf("1: Create a table\n"
"2: Max&Min Number Checking\n"
"3: Negative&Positive Number Checking\n"
"4: Ascending Order\n"
"5: Descending ordert\n"
"6: Exit\n");
printf("Please Choose a number from the list: ");
if (scanf("%d", &a) != 1) /* invalid input */
break;
if (a == 6)
break;
switch (a) {
case 1:
printf("Please Enter The Length Of Your Table ");
if (scanf("%d", &n) != 1)
break;
if (n > 100)
n = 100;
printf("Please Enter Your Table Elements: ");
for (i = 0; i < n; i++) {
scanf("%d", &t[i]);
}
for (i = 0; i < n; i++) {
printf("%d ",t[i]);
}
break;
case 3:
i = 0;
if (t[i] < 0) {
printf("This Number is Negative %d\n", t[i]);
} else
if (t[i] == 0) {
printf("This Number is null %d\n", t[i]);
} else {
printf("This Number is Positive %d",t[i]);
}
break;
}
}
return 0;
}
The current problem is with the Evaluate another interval (Y/N)? prompt. Let's say I run the program 4 times; in order to end it, it requires me to type N 4 times.
int main() {
int trap, test;
double low, hi;
char repeat, c;
//Gather End Points
do {
printf("Enter endpoints of interval to be integrated (low hi): ");
test = scanf("%lf %lf", &low, &hi);
if (test != 2) {
printf("Error: Improperly formatted input\n");
while((c = getchar()) != '\n' && c != EOF); //Discard extra characters
} else
if (low > hi)
printf("Error: low must be < hi\n");
} while ((test != 2 || low > hi));
//Gather amount of triangles
do {
printf("Enter number of trapezoids to be used: ");
test = scanf("%d", &trap);
if (test != 1) {
printf("Error: Improperly formated input\n");
while((c = getchar()) != '\n' && c != EOF); //Discard extra characters
} else
if (trap < 1)
printf("Error: numT must be >= 1\n");
} while ((trap < 1 || test != 1));
//Output integrate
printf("Using %d trapezoids, integral between %lf and %lf is %lf",
trap, low, hi, integrate(low, hi, trap));
//Prompt user for another time
while (1) {
printf("\nEvaluate another interval (Y/N)? ");
scanf(" %c", &repeat);
switch (repeat) {
case 'Y':
main();
case 'y':
main();
case 'N':
return 0;
case 'n':
return 0;
default:
printf("Error: must enter Y or N");
}
}
return 0;
}
I expect it so that no matter what run of the program I'm on it will close when I type one N.
There are many ways to achieve what you want but calling main recursively is not a good idea.
A pretty simple way to change your program is to add an additional while(1) level. Something like:
int main(void)
{
char repeat;
while(1){ // Outer while to keep the program running
printf("running program\n");
// Put your program here
printf("program done\n");
repeat = '?';
while(repeat != 'y' && repeat != 'Y'){ // Repeat until input is 'Y' or 'y'
printf("\nEvaluate another interval (Y/N)? ");
scanf(" %c", &repeat);
switch (repeat){
case 'Y':
case 'y':
break;
case 'N':
case 'n':
return 0; // Stop if input is 'n' or 'N'
default:
printf("Error: must enter Y or N");
}
}
}
return 0; // This will never be reached
}
Another way (a simpler way, IMO) is to put the code where you ask the user into a function that you call from main. Like:
int continueProg()
{
char repeat = '?';
while(1){
printf("\nEvaluate another interval (Y/N)? ");
scanf(" %c", &repeat);
switch (repeat){
case 'Y':
case 'y':
return 1;;
case 'N':
case 'n':
return 0;
default:
printf("Error: must enter Y or N");
}
}
}
int main(void)
{
do {
printf("running program\n");
// Put your program here
printf("program done\n");
} while(continueProg());
return 0;
}
BTW: Take a look at getchar instead of using scanf
There are multiple problems in your program:
You test the return value of scanf() when reading the user's answer to the prompts, and you clear the pending input correctly, but you do not handle the potential end of file, leading to endless loops.
c must be defined as int to accommodate for all values returned by getchar(): 256 values of type unsigned char and the special value EOF.
You can main() recursively to repeat the program's action requiring multiple N answers. You should instead add an outer loop and exit from it upon a N answer or an end of file condition.
Here is a modified version:
#include <stdio.h>
double integrate(double low, double hi, int trap) {
...
}
int flush_line(void) {
// Consume the pending input and return `'\n`` or `EOF`
int c;
while ((c = getchar()) != EOF && c != '\n')
continue;
return c;
}
int main() {
// Main program loop
for (;;) {
int trap, test;
double low, hi;
char repeat;
//Gather End Points
for (;;) {
printf("Enter endpoints of interval to be integrated (low hi): ");
test = scanf("%lf %lf", &low, &hi);
if (test == EOF)
return 1;
if (test != 2) {
printf("Error: Improperly formatted input\n");
if (flush_line() == EOF)
return 1;
continue; // ask again
}
if (low > hi) {
printf("Error: low must be < hi\n");
continue;
}
break; // input is valid
}
//Gather amount of triangles
for (;;) {
printf("Enter number of trapezoids to be used: ");
test = scanf("%d", &trap);
if (test == EOF)
return 1;
if (test != 1) {
printf("Error: Improperly formated input\n");
if (flush_line() == EOF)
return 1;
continue;
}
if (trap < 1) {
printf("Error: numT must be >= 1\n");
continue;
}
break;
}
//Output integrate
printf("Using %d trapezoids, integral between %lf and %lf is %lf\n",
trap, low, hi, integrate(low, hi, trap));
//Prompt user for another time
for (;;) {
printf("\nEvaluate another interval (Y/N)? ");
if (scanf(" %c", &repeat) != 1)
return 1; // unexpected end of file
switch (repeat) {
case 'Y':
case 'y':
break;
case 'N':
case 'n':
return 0;
default:
printf("Error: must enter Y or N\n");
if (flush_line() == EOF)
return 1;
continue;
}
break;
}
}
}
I am implementing a polynomial using array. This is the Problem Statement:
Write a menu-driven program to represent Polynomials as a data structure using arrays. and write functions to add, subtract and multiply two polynomials; multiply a polynomial with a constant, find whether a polynomial is a "zero- polynomial, return the degree of the polynomial. Assume that a new polynomial is created after each operation. How would you input and output polynomials?
I have created the input and output functions. But my do while loop is running twice.. Help me finding out why.
The do-while loop
do{
print_menu();
scanf("%c",&ch);
printf("\nch = %c\n",ch);
switch(ch){
case '1':
create_poly(poly,termpool,&next_poly);
break;
case '2':
print_poly(poly,termpool,&next_poly);
break;
case 'q':
break;
default:
printf("Invalid choice.");
}
}while(ch != 'q');
return 0;
}
The print_menu() function
void print_menu()
{
printf("\n1. Create a new polynomial.");
printf("\n2. Print polynomial.");
printf("\nq. Exit");
printf("\nEnter Choice:");
}
The create_poly() function
void create_poly(int poly[][2], int termpool[][2], int *next_poly)
{
int beg = poly[*next_poly][0];
int end, size, i, j;
printf("Enter size of the polynomial:");
scanf("%d",&size);
poly[*next_poly][1] = beg + size - 1;
end = poly[*next_poly][1];
printf("Enter terms of the polynomial(coeff then exponent):\n");
for(i=beg; i<=end; i++){
for(j=0; j<2; j++){
scanf("%d ",&termpool[i][j]);
}
}
poly[++(*next_poly)][0] = end + 1;
}
The print_poly() function
void print_poly(int poly[][2],int termpool[][2],int *next_poly)
{
int pos,beg,end;
int i;
printf("Enter position of the polynomial:");
scanf("%d",&pos);
if(pos-1 > *next_poly){
printf("Invalid position.");
return;
}
beg = poly[pos-1][0];
end = poly[pos-1][1];
for(i=beg; i<=end; i++){
printf(" %dx^%d +",termpool[i][0],termpool[i][1]);
}
printf("\b = 0");
}
Here is a sample output:
1. Create a new polynomial.
2. Print polynomial.
q. Exit
Enter Choice:1
ch = 1
Enter size of the polynomial:2
Enter terms of the polynomial(coeff then exponent):
2 4
6 7
1. Create a new polynomial.
2. Print polynomial.
q. Exit
Enter Choice:
ch =
Invalid choice.
1. Create a new polynomial.
2. Print polynomial.
q. Exit
Enter Choice:q
ch = q
Tried flushing the stdin… The problem stays. Printing the value of ch in each step, I think it is a whitespace. Where does the white space comes?
The answer to abnormal behavior of scanf answers this question also.
If you test the next code you will note the same problem
int main() {
char c;
do {
scanf_s("%c", &c);
if (c != 'q')
printf("test scanf() function\n");
} while (c);
}
the scanf() function works when the enter key is pressed, but this insert another char in the buffer input, the char of new line '\n', it is taken again by scanf() because the loop block. Try to change the previous code by this code:`
do {
scanf_s("%c", &c); // or c = getchar();
switch (c){
case '\n':
break;
default:
printf("test scanf() function\n");
}
} while (c);`
and will work fine. In your code only add a new case in the switch block:
switch(ch) {
case '1':
create_poly(poly,termpool,&next_poly);
break;
case '2':
print_poly(poly,termpool,&next_poly);
break;
case '\n':
break;
case 'q':
break;
default:
printf("Invalid choice.");
}
sorry, English is not my native language
There's an extra character waiting to be consumed after you make your initial choice, that's why the loop is executing twice.
See this question on the comp.lang.c FAQ