Some backstory
I'm an engineering student (first year) and we had to create a program that could manage a list of students. Basically putting information of students in an array of structs (student name, birth date, grades). It had to be possible to add students, delete students, sort students, change information, add grades, save progress, load progress and generate a mark list(html/css).
My problem
I wanted to add settings to my project. I put some information in a file I called settings.txt. The first and second line are integers and can be 1 or 0. The third line is a string. Creating this file and reading from the file works fine, but of course I wanted the user to be able to change his settings too. However, when I run the code below, my .exe crashes. It's probably because of something stupid I'm doing but I've been looking at this for a couple of hours now and my 'fixes' make things worse. I hope someone can help me, thanks in advance! :)
I tried adding some comments in english, originally the outputs in printf were dutch. If anything is unclear, please ask!
Code
char getBool (char option[], char booly[]) {
if (option[0]!='0') {
strcpy(booly,"true");
} else {
strcpy(booly,"false");
}
}
char editSettings (char settings[], char startLoad[]) {
//This function will allow the user to edit some settings
//Declare variables: file: filename, lijn: storage for xth line of file,booly: true/false output. Settings:reset: 1/0,load: 1/0,startfile: filename
char file[15]="settings.txt",lijn[25],booly[10],reset,load,startfile[25];
int inp,i;
do {
i=1;
//Read file and output current settings to user
FILE * bestand;
bestand=fopen(file,"rt");
fgets(lijn,999,bestand);
while (!feof(bestand)) {
//i determines what line we're on -> There are always 3 lines
//1st line can be 0 or 1 -> Reset screen after cmd?
//2nd line can be 0 or 1 -> Load file
//3th line is a string (filename) -> .txt is automatically added when loading file
getBool(lijn,booly);
if (i==1) {
printf("%d - Reset screen after every command: %s\n",i,booly);
reset=lijn;
} else if (i==2) {
printf("%d - Load file on startup: %s\n",i,booly);
load=lijn;
} else if (i==3) {
strcpy(startfile,lijn);
}
fgets(lijn,999,bestand);
i++;
}
fclose(bestand);
printf("Pick a setting to change or enter 0 to cancel.\nChoose: ");
//Let user choose a value: 0, 1 or 2. Anything else won't
inp=inlezen("012");
printf("\n");
//Process users choice
if (inp=='1') {
//Toggle reset option, remain other options
bestand=fopen(file,"wt");
if (reset=='0') {
reset='1';
} else if(reset=='1') {
reset='0';
}
fprintf(bestand,"%s\n",reset);
fprintf(bestand,"%s\n",load);
fprintf(bestand,"%s\n",startfile);
fclose(bestand);
} else if (inp=='2') {
//Toggle load on startup option + read filename to start, remain reset option
bestand=fopen(file,"wt");
if (load=='0') {
load='1';
} else if(load=='1') {
load='0';
}
fprintf(bestand,"%c\n",reset);
fprintf(bestand,"%c\n",load);
if (load=='1') {
printf("\nWhich file must be loaded on startup?\nGive name: ");
scanf("%s",&startfile);
}
fprintf(bestand,"%s\n",startfile);
fclose(bestand);
}
} while (inp!='0');
printf("\n");
}
However, when I run the code below, my .exe crashes.
You define char …reset,load, and then you pass those characters to fprintf() with the wrong conversion specifier s:
fprintf(bestand,"%s\n",reset);
fprintf(bestand,"%s\n",load);
If your compiler didn't warn about inconsistent usage of those variables, you should use a better compiler; if it did, you should pay attention to the warnings.
Related
I'm fairly new to C (high school student), and my goal is to make a grocery list by inputting a set of characters. Then, the output would print out what I currently added to the list. This would go on forever until I exited the program or went to the main menu.
SCREEN1
00 - GO TO GREETINGS SCREEN
01 - ADD MORE ITEMS TO THE LIST
CODE ENTRY: ___
SCREEN2
Then I entered 01 to add items:
Input "DONE" to end program and see final list.
LIST ENTRY: ______________
SCREEN3
Then I add "apples", then it takes me to this screen:
GROCERY LIST:
POTATOES
FISH
APPLES
After that, it takes me back to SCREEN1, where I would choose whether to go to the greetings screen or add some more.
MY CURRENT CODE:
#include <stdio.h>
#include<stdlib.h>
int main()
{
int n;
char * grocery;
mainMenu:
system("cls");
n = 0;
printf("00 - Go to greetings screen\n01 - Add groceries to list\nENTRY: ");scanf("%d",&n);
if(n == 0)
{
greetings();
goto mainMenu;
}
else if(n == 1)
{
printf("GROCERY ENTRY: ");scanf("%s",grocery);
add(grocery);
goto mainMenu;
}
else
{
printf("Wrong value added. Try again.");
sleep(2);
goto mainMenu;
}
}
void greetings()
{
system("cls");
printf("hello! press any key to go back to menu");
getch();
system("cls");
}
void add(char * a)
{
system("cls");
char listData[1000] = "",slashN[4] = "\n";
strcat(listData,a);
strcat(listData,slashN);
printf("THINGS TO BUY:\n");
puts(listData);
}
NOTES
I used strcat so that it remembers the value of the original string. This'll make sure that the new input will just be put on top of the old data, right? (Hopefully, my logic is correct on that one)
Though, I have not been able to find out whether or not the string data will still be remembered by the program even if I am switching to other menus, such as the Greetings Menu (which is a placeholder for something like a calculator).
Right now, the initial functions work, except for the the grocery list one. Whenever I input a string, nothing comes out of it, even the printf("THINGS TO BUY:") part, leading me to think it's something with what I entered in void add(char * a)
After trying out your code, I received a segmentation fault where you have scanf("%s",grocery);. Try allocating space to the variable, using malloc(3) (see http://man7.org/linux/man-pages/man3/malloc.3.html). For example, char *grocery = (char *)malloc(sizeof(char) * 100); will give you 100 characters to read into your grocery variable from input.
The same objective can also be achieved by simply using char grocery[100]; as you have with other variables.
Furthermore, as many programmers would suggest, try not to use goto(). This can cause spaghetti code (see https://en.wikipedia.org/wiki/Spaghetti_code). Instead, use a while loop that stops only when the user inputs some action designed to stop entering requests.
Lastly, just so you avoid unwarranted results, \n is actually a single character. Therefore, char slashN[4] = "\n" can be char slashN = '\n';.
Happy coding! :D
the data on the file.txt are placed as shown.
My Code is this:
int searchBookname()
{
FILE *myFile=fopen("file.txt","r+");
if (myFile!=NULL) // file exists
{
char tmp1[512];
char tmp2[512];
while(fgets(tmp1,512,myFile)!=EOF)
{
puts("Insert the Book Name: ");
scanf("%s",tmp2);
if(strstr(tmp1,tmp2)!=NULL){
printf("the book is found: %s\n\n",tmp1);
}else{
puts("\nSorry there was no Match with this name! Maybe Book is not recorded yet :(\n");
}
}
}else{ // file doesn't exist
puts("\nDatabase is not created yet. Please record a new book to create a simple database\n");
exit(0);
}
fclose(myFile); // closing the file
}
It keeps skipping the if statement 2 times for some reason and on the
3rd time it prints the correct result.
This happen for whatever book I try to search.
See here
How can I make it find the result without skipping the if statement.
You read the file line by line. So in the third loop/line there is a record with 'book1'. Code is working correctly as it is. Maybe you want to ask the user for a book name outside of the while loop and search in every line for the given book name. If there is, you can print you message and break from the loop.
int searchBookname()
{
FILE *myFile=fopen("file.txt","r+");
if (myFile != NULL) // file exists
{
char tmp1[512], tmp2[512];
puts("Insert the Book Name: ");
scanf("%s",tmp2);
// Skip the first two lines of the file
fgets(tmp1,512,myFile);
fgets(tmp1,512,myFile);
while(fgets(tmp1,512,myFile) != EOF)
{
if(strstr(tmp1,tmp2) != NULL)
{
printf("the book is found: %s\n\n",tmp1);
break;
}
else
{
puts("\nSorry there was no Match with this name! Maybe Book is not recorded yet :(\n");
}
}
}
else
{ // file doesn't exist
puts("\nDatabase is not created yet. Please record a new book to create a simple database\n");
exit(0);
}
fclose(myFile); // closing the file
}
It is obvious.
First 2 lines of file are following:
Record_Date ...
-> (empty line)
You are reading file line by line and check book name in each line. So if must fail for first 2 times.
If you want to find a book in your file, your approach is incorrect. There are different approaches for this, but simplest is reading book records into an structure array, and then look for book name in that array.
I have an assignment due and I am drawing a blank on what exactly to do... I'm sure it is simple but I havent quite gotten the hang of things yet. The assignment is -
Write a program that gives the user 2 menu options: either call a function that will print a greeting and your name 4 times or call a function that will count down from 10 to 0 and then print "Blastoff!". Both functions should use for loops to print the appropriate output.
I have the prompt and the functions done so far... but I am unsure of how to display one or the other depending on the choice the user makes. Thank you for your help.
#include <stdio.h>
int main (void){
// declare counter variable
int i;
// prompt the user to make a choice
printf("What would you like to do?\n 1. Print my name\n 2. Count down from 10\n");
printf("\n");
// display greeting and name 4 times
for(i=1;i<=4;i++)
{
printf("Hi, my name is Bridget\n");
}
// display countdown
for(i=10;i>=0;--i)
{
printf("%d\n", i);
}
printf("Blastoff!");
}
You should read the input from user's keyboard:
int c;
c = getchar();
if (c == '1')
{
// display greeting and name 4 times
for(i=1;i<=4;i++)
{
printf("Hi, my name is Bridget\n");
}
}
if (c == '2')
{
// display countdown
for(i=10;i>=0;--i)
{
printf("%d\n", i);
}
}
printf("Blastoff!");
you should use Switch case.
switch(choice) {
case 1: //first for loop
break;
case 2: //second for loop
break;
}
Looks like you are missing a couple of points here. Firstly, you have not yet written any functions. Try looking here to gain some insight on that front.
Secondly, to make a choice based on user input you need to actually get that input somehow. You'll probably want to use scanf.
Lastly, once you have the user's input (say, in a variable declared as int input;) you can use if to control the flow of your program based on that variable like this:
if(input == 1){
greet();
}
else {
countDown();
}
Cheers! If you have any further questions feel free to comment below.
First of all you haven't actually declared you functions. Functions in C should be declared like the main function is. For more info in this see here.
// display greeting and name 4 times
void greeting(){
for(i=1;i<=4;i++)
{
printf("Hi, my name is Bridget\n");
}
}
void countdown() {
// display countdown
for(i=10;i>=0;--i)
{
printf("%d\n", i);
}
printf("Blastoff!");
}
To get the user's input the most common way is by keyboard. scanf accomplishes that in C. Details on scanf here
int main(void){
int i, choice;
//prompt the user to make a choice
// You don't need 2 printf for the newlines stick them to one.
printf("What would you like to do?\n 1. Print my name\n 2. Count down from 10\n\n");
//This takes the user's input and puts it in the variable choice
scanf(%d, &choice);
}
Lastly to decide what to do based on the user input you can use either an if then else statement or a switch. I will provide a solution with an if statement and you can figure the one with the switch on your own. Your final code should look like this.
int main(void){
int i, choice;
//prompt the user to make a choice
// You don't need 2 printf for the newlines stick them to one.
printf("What would you like to do?\n 1. Print my name\n 2. Count down from 10\n\n");
//This takes the user's input and puts it in the variable choice
scanf(%d, &choice);
if(choice == 1){
greeting();
}else{
countdown();
}
}
// display greeting and name 4 times
void greeting(){
for(i=1;i<=4;i++)
{
printf("Hi, my name is Bridget\n");
}
}
void countdown() {
// display countdown
for(i=10;i>=0;--i)
{
printf("%d\n", i);
}
printf("Blastoff!");
}
Bear in mind that this code has a lot of flaws (error checking mainly) but I guess your assigment is not about that.
First of all you need to include libraries with function you will need. You do this by
#include <someLibrary.h>
at the beggining of you document. Libraries mostly have .h extension. Always look for them if you try to do something. You consider them to have best performance and functionality as possible (not always true).
What is next you declare your functions. Function has name, arguments which are going into it, body in which they do something and return value (can be float, int, char etc). If function doesnt return anything, they return void (dont have return at the end). You declare functions before main() with only types of arguments. Whole body is after main (it is better looking).
If you declared function with arguments, you have to provide these arguments to function in () brackets. Even if no arguments are needed, you use them like getch() in example below. Note that function become what it return. If you declared some new variables in function they will be visible only in function. On the other hand function will not see any variable from other function (main too). If you want so, declare global variables (not recommended).
#include <stdio.h>
#include <conio.h> //libraries
void function1(int);
float function2(float); //declaration of functions
int main()
{
char decision;
printf("press 'a' to run function1, press 'b' to run function2\n");
decision=getch(); //first see getch()? look in google for functionality and library !
int someInt=10;
float someFloat=11;
if(decision== 'a')
{
function1(someInt);
}
else if(decision == 'b')
{
printf("%f", funcion2(someFloat)); //example that function become what they return
}
else
{
printf("No decision has been made");
}
getch(); //program will wait for any key press
return 0;
}
void function1(int param1)
{
//print your stuff // this function return void, so doesnt have return; statement
}
float function2(float param1)
{
return 2*param1; //this function have to return some float
}
I have written the following function in my C program. The program loads a text file (Les Miserables Vol. I) as well as another text file of 20 of the characters names. The purpose of this function is to scan the entire file, line by line, and count the number of times any of the 20 names appear.
NumOfNames = 20.
Names is an array of the 20 names stored from Names[1] - Names[20].
MaxName is a global integer variable which I would like to store the total number of name appearances throughout the file (It should be in the hundreds or even thousands).
EDIT: After the function is executed, the value of MaxName is 4. I am completely lost as to where I have made a mistake, but it appears that I have made several mistakes throughout the function. One seems to be that it only executed the first iteration of the for loop i.e. it only searches for Name[1], however the first name appears 196 times in the file, so it still isnt even working correctly for just the first name.
void MaxNameAppearances()
{
char LineOfText[85];
char *TempName;
FILE *fpn = fopen(LesMisFilePath, "r+");
for(i = 1; i<=NumOfNames; i++)
{
while(fgets(LineOfText, sizeof(LineOfText), fpn))
{
TempName = strstr(LineOfText, Names[i]);
if(TempName != NULL)
{
MaxName++;
}
}
}
fclose(fpn);
}
I guess that one problem of the code is that it would have to read the file upon every iteration of i. Try to re-order the loops like this:
while(fgets(LineOfText, sizeof(LineOfText), fpn))
{
for(i = 1; i<=NumOfNames; i++)
{
TempName = strstr(LineOfText, Names[i]);
if(TempName != NULL)
{
MaxName++;
}
}
}
This reads a line, checks the occurrances of all names in that line and then goes on to the next line.
If you do it your way, you will be at the end of file for i == 1 already.
I'm making a small console-based rpg, to brush up on my programming skills.
I am using structures to store character data. Things like their HP, Strength, perhaps Inventory down the road. One of the key things I need to be able to do is load and save characters. Which means reading and saving structures.
Right now I'm just saving and loading a structure with first name and last name, and attempting to read it properly.
Here is my code for creating a character:
void createCharacter()
{
char namebuf[20];
printf("First Name:");
if (NULL != fgets(namebuf, 20, stdin))
{
char *nlptr = strchr(namebuf, '\n');
if (nlptr) *nlptr = '\0';
}
strcpy(party[nMember].fname,namebuf);
printf("Last Name:");
if (NULL != fgets(namebuf, 20, stdin))
{
char *nlptr = strchr(namebuf, '\n');
if (nlptr) *nlptr = '\0';
}
strcpy(party[nMember].lname,namebuf);
/*Character created, now save */
saveCharacter(party[nMember]);
printf("\n\n");
loadCharacter();
}
And here is the saveCharacter function:
void saveCharacter(character party)
{
FILE *fp;
fp = fopen("data","a");
fwrite(&party,sizeof(party),1,fp);
fclose(fp);
}
and the loadCharacter function
void loadCharacter()
{
FILE *fp;
character tempParty[50];
int loop = 0;
int count = 1;
int read = 2;
fp= fopen("data","r");
while(read != 0)
{
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
printf("%d. %s %s\n",count,tempParty[loop].fname,tempParty[loop].lname);
loop++;
count++;
}
fclose(fp);
}
So the expected result of the program is that I input a name and last name such as 'John Doe', and it gets appended to the data file. Then it is read in, maybe something like
1. Jane Doe
2. John Doe
and the program ends.
However, my output seems to add one more blank structure to the end.
1. Jane Doe
2. John Doe
3.
I'd like to know why this is. Keep in mind I'm reading the file until fread returns a 0 to signify it's hit the EOF.
Thanks :)
Change your loop:
while( fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp) )
{
// other stuff
}
Whenever you write file reading code ask yourself this question - "what happens if I read an empty file?"
You have an algorithmic problem in your loop, change it to:
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
while(read != 0)
{
//read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
printf("%d. %s %s\n",count,tempParty[loop].fname,tempParty[loop].lname);
loop++;
count++;
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
}
There are ways to ged rid of the double fread but first get it working and make sure you understand the flow.
Here:
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
printf("%d. %s %s\n",count,tempParty[loop].fname,tempParty[loop].lname);
You are not checking whether the read was successful (the return value of fread()).
while( 1==fread(&tempParty[loop],sizeof*tempParty,1,fp) )
{
/* do anything */
}
is the correct way.
use fopen("data","rb")
instead of fopen("data","r") which is equivalent to fopen("data","rt")
You've got the answer to your immediate question but it's worth pointing out that blindly writing and reading whole structures is not a good plan.
Structure layouts can and do change depending on the compiler you use, the version of that compiler and even with the exact compiler flags used. Any change here will break your ability to read files saved with a different version.
If you have ambitions of supporting multiple platforms issues like endianness also come into play.
And then there's what happens if you add elements to your structure in later versions ...
For robustness you need to think about defining your file format independently of your code and having your save and load functions handle serialising and de-serialising to and from this format.