So here is my first ultra beginner computer programming question in C.
I need to set it up so that someone can type in their full name on the input. Here is part of the specs -
"You'll have to do a little thinking to figure out how to get the printed names lined up with all the other columns. The first hint is that it involves joining strings together, something called concatenation. Give it a go, and if you can't figure it out, look at the next document in this folder; it contains additional hints. Part of the purpose of this assignment is to implicitly teach you concatenation. Do NOT use tabs (\t) and make sure your C/C++ editor does not produce tab characters.
Do NOT use gets() in this program. Use scanf() for inputting the interactive information. If you try to use gets(), you may get VERY frustrated.
In essence, all numbers appearing in the report should be right-justified and decimal-aligned. All numbers appearing in the summary should appear without leading spaces (other than the one which normally separates the number from the previous word). Hourly wage amounts CAN be less than 10.00, so be very careful with your formatting. The sample output can appear correct, but you can still be docked a half-point if things don't align properly with hourly wages under $10.00."
Additional hints:
You may assume that the employee name is always two names, a first name and a last name separated by a space. Also assume that there are never any spaces within a first name or within a last name. This allows you to use two scanf() calls instead of one gets() call. gets() would introduce some oddities that make things not work correctly later down the line.
You may also assume that neither name exceeds 10 characters in length.
The input from the Process another employee? question should be a single character. Assume that N or n will stop the loop, but that any other character will continue the loop.
Anyone know how to do this? When I use gets(which he says not to do), the loop screws up on the 2nd time around and it asks for the name and salary all in one line. And if I try to use 2 scanf statements, I get a crash or only 1 of the names input.
I was thinking the only way to do it is by outputting the names to a text file, then reading them in again. But is there some other way? I'm not allowed to ask for the names individually. A user might type a full name with one space, as it says in the specs.
Here is the code I wrote so far. I also need totals for all the gross', overtime hours and regular hours.
//stupid program
#include <stdio.h>
#include <strings.h>
#include <math.h>
//global variables
FILE *reportfile; //output file
char department[21];
int count;
char name[21];
float hoursworked;
float hourlywage;
float overtimehoursworked;
float overtimehourlywage;
float gross;
char again;
char firstname;
char lastname;
float tothoursworked;
float totovertimehoursworked;
float totgross;
const float overtimerate = 1.5;
const float overtimethreshold = 40; //hours needed to get overtime
//function prototypes
void GetInfo(void);
void Finalreport(void);
//main
int main(void)
{
reportfile = fopen("c:\\class\\kpaul-pay.txt","w"); //open output file
//////////////////////////////////////////////////
// initialize accumulating variables
/////////////////////////////////////////////////
count = 0;
tothoursworked = 0;
totovertimehoursworked = 0;
totgross = 0;
GetInfo();
fclose(reportfile); //close output file
return 0;
}
void GetInfo (void)
{
printf("Mountain Pacific Corporation\n");
printf("Department Salary Program\n\n");
printf("Please enter the name of the department: ");
gets(department);
fprintf(reportfile, "Mountain Pacific Corporation\n");
fprintf(reportfile, "Department Salary Program\n\n");
fprintf(reportfile, "%s\n\n", department);
fprintf(reportfile, "Employee Reg Hrs Overtime Hrs Gross\n");
fprintf(reportfile, "-----------------------------------------------------------------\n");
do {
printf("\nEnter employee #1: ");
gets(name);
printf("Enter the hourly wage of %s", name);
scanf("%f", &hourlywage);
printf("\nEnter total number of hours: ");
scanf("%f", &hoursworked);
if (hoursworked<=overtimethreshold)
overtimehoursworked = 0;
else if (hoursworked > overtimethreshold)
overtimehoursworked = hoursworked - overtimethreshold;
gross = (hoursworked*hourlywage) + (overtimehoursworked*overtimehourlywage);
fprintf(reportfile, "%s%16.2f(%4.2f)%12.2f(%4.2f) $%7.2f", name, hoursworked, hourlywage, overtimehoursworked, hourlywage * overtimerate, gross);
tothoursworked = tothoursworked + hoursworked;
totovertimehoursworked = totovertimehoursworked +overtimehoursworked;
totgross = totgross + gross;
printf("\n");
printf("Would you like another conversion? ");
scanf ("%s", &again);
printf("\n\n");
} while (again!='N' && again!='n');
}
Careful use of the scanf format string is needed. %s indicates a string that is delimited by a white space, in non technical terms, scanf will read characters until it finds a whitespace character such as a tab or space.
This poses a problem for reading multiple words, this can be solved by using multiple %s in the format string, you must provide a seperate array for each word as an argument after the format string e.g.
scanf("%s%s%s", string1, string2, string3)
This scanf call expects three words from the user, where each word is delimited by a white space. Make sure there is allocated memory for each of arrays though otherwise you will write into memory the program does not own normally causing the program to crash. The exact same effect to the code above can be achieved by using scanf multiple times with a single %s in the format string.
If you need everything as one string the same array you can use strcat which will concatenate two strings together. The function is simple to use, but once again make sure your arguments are allocated arrays before calling strcat otherwise it will likely cause a crash or unexpected behaviour.
Here are references to both functions:
scanf - http://www.cplusplus.com/reference/clibrary/cstdio/scanf/
strcat - http://www.cplusplus.com/reference/clibrary/cstring/strcat/
Hope this helps =]
scanf with the format %s will accept a whitespace-delimited string.
The crash is most likely caused by overflowing (or failing to reserve space for) the input string.
Related
I am new to C, so excuse me for asking a seemingly easy question. but I have a loop which loops depending on the user, and inside the loops it asks for a name and an age, however when I go to print, it only prints the last entry and not all the entries I want.
#include <stdio.h>
int main()
{
int size,age;
char name [30];
printf("How long to loop for: ");
scanf("%d", &size);
for (int i=0; i<size; i++)
{
printf("Enter first name: ");
scanf("%s", name);
printf("Enter %s's age: ",name);
scanf("%d",&age);
printf("name: %s, age: %d\n", name,age);
}
return 0;
}
Right now your name and age variables will only hold the last input they received, thats why you're program only prints the last index. You need an array of int as well as an array of char [] to "hold" each input they receive, otherwise those inputs get lost and you only get input for the last index.
your variables should be initialized like:
int size;
printf("Enter size: ");
scanf("%d", &size);
int age [size];
char name[size][30];
in order to get user input and print each entry you will need to access each index by looping through the array size.
to access each index:
age[i]
name[i]
Please Note: using scanf to get a string from user input is generally bad, as it can cause problems if you happen to use a space(such as inputting your full name for example) in your input, and it can cause a buffer overflow if your string is longer than the buffer. Instead you can use fgets, but for your question it isn't necessary, just something to considered in the future in case you want to have spaces in your inputs.
Are you sure that the first scanf actually reads a number.
You want the following to check
if (scanf(" %d", &size) != 1) { // Note space - Eats white space/new lines
printf("Error - invalid size\nExiting\n");
return -1;
}
Prevent buffer overruns
Use:
scanf(" %29s", name); // See above
See point 1 for age
I think this will solve your problems
Okay so if I am understanding you correctly, you are looping through the for loop size number of times and each time you are setting the contents of the variables age and name. It sounds like you are expecting each iteration through the loop to save your entered instance of age and name but this is not the case.
Since you only have one age and one name variable they are going to store whatever the most recently taken input was. So this means whatever was entered on the last loop is what was last written into the variables name and age.
If you then try to print the contents of those variables you are going to see whatever was most recently entered into those variables. you would need more than one name and more than one age variable to write into if you were trying to save multiple entries.
Okay so Anthony, maybe you need to try a little bit of review when it comes to allocating memory. So when we declare the variable
int age;
we are telling the compiler to allocate enough memory to store one single integer that we will call 'age' in our program. since we only asked for enough memory to store one integer, every time you scanf() into the age variable, the single integer is written into that space.
What you want is to store a new integer every time you do another run through your for loop. So, you could declare an array of integers as follows.
int age[20];
Now we have asked the compiler to allocate enough space to store 20 different integers. there will an integer in position age[0] and another integer in age[1] and another in age[2] so on. So now you could use a loop to index through your array and store each entered age from stdin into a different position in the array as follows
for(int i=0; i<20; i++)
{
printf("Please enter your age: ");
scanf("%i", &age[i]);
}
So this loop starts with i=0 and so enters the input from stdin to age[0], the next iteration through the loop has i=1 and so enters the stdin input to age[1] and so on.
Hopefully this clarifies things a bit more?
A major fault is that your printfs will not be displayed as they are buffered.
You need a fflush after them
i.e.
printf("How long to loop for: ");
fflush(stdout);
And
printf("Enter first name: ");
fflush(stdout);
etc...
I'm pretty new to C and I'm working on a simple practice problem with structures. My code asks for input termed "employee information", asking for their name (a string), the date they were hired (a string) and what the salary will be (an integer).
The first fgets works fine, and sticks a newline in the buffer as usual. The second then takes input and promptly jumps out the program.
I've tried sticking extra scanf()'s and getchar()'s in lots of different places to get rid of the newline, but nothing seems to help.
I even tried all of this with the debugger, and the only thing I get is a segmentation fault, which I don't really understand.
I have looked around, asked people and nothing seems to solve this problem. I am more than aware of all the questions similar to this one, but for some reason I just can't get it to work.
#include <stdio.h>
#include <stdlib.h>
/*****
Initialize a structure to read in and record the employee name, the hire
date and their salary
******/
//Define structure
struct employee
{
char *name;
char *hireDate;
float salary;
};
int main()
{
//First hardcode an employee
struct employee emp1;
emp1.name = "Karl";
emp1.hireDate = "May 10, 2019";
emp1.salary = 60000.00f;
//Now print off this employee
printf("The first employee's name is %s, he was hired on %s and will make %f per year\n", emp1.name, emp1.hireDate, emp1.salary);
printf("The next employee is you! Please enter the following information\n");
//Now ask user for second employee
struct employee emp2;
printf("Please enter your name: \n");
fgets(emp2.name, 30, stdin);
//This one works just fine, it produces name\n
printf("Please enter the date you were hired in regular format (i.e. May 10, 2019)\n");
//I had hoped this scanf() would absorb the above newline
scanf(" ");
//This takes input, and then jumps out of the program
fgets(emp2.hireDate, 30, stdin);
printf("Please enter your salary: \n");
scanf(" ");
scanf(" %f",&emp2.salary);
//Now print off this stuff that was typed in
printf("The first employee's name is %s, he was hired on %s and will make %f per year\n", emp2.name, emp2.hireDate, emp2.salary);
return 0;
}
You shouldn't declare those pointers like that unless you malloc() memory for them at some point. Since you're limiting your input to 30 chars statically you should declare your strings inside the struct as arrays: char name[31] and char hireDate[31]. You need that extra char in your arrays to hold the '\0' which terminates the string.
Please remember that fgets() takes the buffers size as 2nd parameter, not the number of characters to read. To allow the user to input a maximum of 30 characters you'd pass 31 as 2nd argument to fgets().
You don't have allocated memory to store the values read by gets.
In emp2, the pointers are not initialized, the first call to fgets could also segfault.
You need to allocate memory to hold the values, either by using malloc, or by defining your string fields as char name[30] for example.
My goal with this program is to incorporate the users inputs into a sort of interactive/randomized story but I'm not sure how I'm supposed to get the inputs from the users to fit between *ptrDescription, *ptrBeginning, *ptrMiddle, and *ptrEnd. Any help would be much, much appreciated!
#include <stdio.h>
#include<stdlib.h>
#include<time.h>
#include <string.h>
#include <ctype.h>
int main(void){
int i;
char name[20];
char color[20];
int age;
char sentence[1];
//array of pointers to char arrays
char *ptrDescription[]={"the painfully handsome","the one and only","who seemed much older than"};
char *ptrBeginning[]={"was blissfully ignoring","could clearly see","had no idea"};
char *ptrMiddle[]={"the huge truck","the falling meteor","the bucket of milk","the mailman","the most powerful wizard"};
char *ptrEnd[]={"that was barreling toward them.","on the horizon."};
srand(time(NULL));
printf("Enter your first name: ");
scanf("%s", &name);
printf("\nEnter your age: ");
scanf("%d", &age);
printf("\nEnter your favorite color: ");
scanf("%s", &color);
for (i = 0; i < 1; i++)
{
//strcpy(sentence,ptrDescription[rand()%3]);
//strcat(sentence," ");
//strcat(sentence,ptrBeginning[rand()%3]);
//strcat(sentence," ");
//strcat(sentence,ptrMiddle[rand()%5]);
//strcat(sentence," ");
//strcat(sentence,ptrEnd[rand()%2]);
//strcat(sentence,".");
//sentence[0]=toupper(sentence[0]);
puts(sentence);
}
getch();
return 0;
}
EDIT:
I've edited a section of my code so that directly following for (i = 0; i < 1; i++) it now looks like this:
snprintf(sentence, sizeof sentence,"%s, %s %d year old, %s %s %s %s", name, ptrDescription[rand()%3], age,ptrBeginning[rand()%3], ptrMiddle[rand()%5], ptrEnd[rand()%2]);
There are tons of strange characters after the sentence in the output, like Japanese characters and stuff. I'm not sure why they're there, though. This is what it looks like exactly:
"Enter your first name: Justin
Enter your age: 20
Justin, the arrogant 20 year old, was purposefully ignoring the most powerful wizard that was barreling toward them. 汽$0HβHζ(ﾃﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌH・(DｷHH広$0陏&・汽$0ﾀHζ(ﾃﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌﾌH WH・ H櫛H・t9HνHﾃ<"
Anyone know how I can get rid of them?
If you already have a name and an age, it's just a matter of inserting them into the correct place in sentence, right? So strcat(sentence, name) would work for name. age is a little trickier since you have to format the number first, and strcat won't do it for you. One solution would be to use sprintf(buf, "%d", age), and then concatenate buf (which is a scratch char array you would have to declare).
Any time you work with strings in C, you have to be concerned about having enough space in the target buffer. Your program can run out of space during both input and output. For the output, I would get rid of sentence altogether; since you just end up writing to stdout I would printf("%s", [part]) each part as you go along. For reading, scanf supports adding a length argument to the format string.
If you use one of the *printf functions, there are 2 things you must be careful about:
The arguments you pass are correct for the format string you use
Your buffer ends up null-terminated
Your current problem is with #1 - your format string promises 7 arguments to follow, but you only supply 6. snprintf grabs a "random" 7th value from the stack, interprets it as a char pointer, and copies whatever it finds there to sentence. You could see similar problems if your format string promised a char pointer but you placed an int in a given position. In this case the format string is a constant, so a smart compiler can validate that your format string matches the subsequent parameters. You'll want to get into the habit of taking compiler warnings seriously and not ignoring them.
The second point could be an issue if your sentence ended up bigger than your sentence buffer. If there is no room for a null-terminator, one won't be applied. You can check the return value of snprintf, or you can defensively always write a 0 to the last array position.
I am writing a super simple command line based program in C. It's just a small test and the code is very simple. So what it is meant to do is to ask the user for their name, maths grade, english grade, computing grade. Then it figures out their average grade and also tells them the name they entered. Yes I know this is an extremely simple program, but I'm still doing something wrong.
The problem is, one part of my code will run first telling the user to enter their name and then once they do this and press enter the rest of my code will run all at once and then stop working. It's weird I just don't understand what is wrong.
#include <stdio.h>
int main(int argc, const char * argv[])
{
char chr;
char firstname;
int mathsmark, englishmark, computingmark, averagemark;
printf("What is your name?\n");
scanf("%c", &firstname);
printf("\n");
printf("What is your maths mark?\n");
scanf("%d", &mathsmark);
printf("\n");
printf("What is your english mark?\n");
scanf("%d", &englishmark);
printf("\n");
printf("What is your computing mark?\n");
scanf("%d", &computingmark);
printf("\n");
printf("Your name is: %c", firstname);
printf("\n");
averagemark = (mathsmark + englishmark + computingmark) / 3;
printf("%d", averagemark);
printf("\n");
chr = '\0';
while (chr != '\n') {
chr = getchar ();
}
return 0;
}
One major problem is that you've declared firstname to be a single character long, and when you try to read the name from the console, you're using the %c conversion specifier, which reads the next single character from the input stream and stores it to firstname. The remainder of the name is left in the input stream to foul up the remaining scanf calls.
For example, if you type "Jacob" as a first name, then the first scanf call assigns J to firstname, leaving "acob\n" in the input stream.
The next scanf call attempts to convert "acob\n" to an integer value and save it to mathsmark, which fails ("acob\n" is not a valid integer string). Same thing happens for the next two scanf calls.
The last loop
while (chr != '\n')
{
chr = getchar();
}
finally consumes the rest of "acob\n", which contains the newline character (because you hit Enter after typing the name), causing the loop and program to exit.
How do you fix this?
First, you need to declare firstname as an array of char:
char firstname[SOME_SIZE] = {0};
where SOME_SIZE is large enough to handle all your cases. The you need to change scanf call to
scanf("%s", firstname);
This tells scanf to read characters from the input stream up to the next whitespace character and store the results to the firstname array. Note that you don't need to use the & operator here; under most circumstances, an expression of array type will be converted ("decay") to an expression of pointer type, and the value of the expression will be the address of the first element in the array.
Note that scanf is not very safe, and it's not very robust. If you enter more characters than your buffer is sized to hold, scanf will happily store those extra characters to memory following the array, potentially clobbering something important. You can guard against this by using an explicit field width in the conversion specifier, like
scanf(*%29s", firstname);
but in general it's a pain.
scanf is also not very good at detecting bad input. If you enter "12er" as one of your marks, scanf will convert and assign the "12", leaving the "er" in the stream to foul up the next read.
scanf returns the number of successful assignments, so one way to guard against bad input is to check the return value, like so:
if (scanf("%d", &mathmarks) != 1)
{
printf("Bad input detected for math marks\n");
}
Unfortunately, scanf won't remove bad characters from the stream; you'll have to do that yourself using getchar or similar.
This is a common mistake amongst newer C/C++ developers. The scanf function detects you hitting the ENTER/RETURN key to signal the end of input, but it also catches the \n character as well at the end of the input string, so you essentially get two RETURNS being detected.
Please read up on an example of using fgets and sscanf here:
http://www.linuxforums.org/forum/programming-scripting/67560-problem-scanf.html
It will resolve this issue very quickly for you. In the meantime, I strongly urge you to check out this book:
http://www.amazon.com/Primer-Plus-5th-Stephen-Prata/dp/0672326965
It is the most commonly used C programming book in high school and colleges in North America, and has TONS of examples for you to work through, including this specific program you demonstrated above. The print version has more examples than the e-book, so I would just cough up the $30.00 for the printed version.
Good luck!
You might want to look at a few tutorials. Maybe one on Format specifiers and one on strings in C
scanf() reads data from stdin and stores them as specified by the format specifiers. In this case:
char firstname;
scanf("%c", &firstname);
Read 1 character from stdin and store it to firstname:
>> What is your first name?
Mike
Now firstname == 'M' because scanf() read 1 character as we requested.
What you wanted to do was read a string (a bunch of characters):
char firstname[5]; // an array of characters
scanf("%s", firstname); // store as a string
firstname[4] = '\0'; // Truncate the result with a NULL to insure no overflow
>> What is your first name?
Mike
Now firstname is [M][i][k][e][\0] because scanf() read 1 string, as we requested.
Note the same holds true for printf(), a printf with a %c will give you one character where as a printf() with a %s will give you all the characters until the NULL terminator.
You have (at least) two choices.
char firstname[number_big_enough_to_hold_long_name];
/*or */
char *firstname = malloc(sizeof(char) * number_big_enough_to_hold_long_name);
/* ... code ... */
free(firstname);
Further it would be best to limit width of read. scanf() does not know the size (available space) of firstname.
scanf("%number_big_enough_to_hold_long_names", ...
/* i.e. */
char firstname[32];
if(scanf("%31s", firstname) == EOF) {
perror("bad");
return 1;
}
Further you should check if there is anything left before trying next read. I.e. If someone enters "My Name" then only "My" will end up in firstname and "Name" will be left in input stream.
And getchar() returns an int not a char.
getchar
scanf
And search "ansi c char arrays tutorial" or similar.
Hey,
I'm trying to get this function to get the following output with the listed input, the "..." is where I'm not sure what to write:
void Question8(void)
{
char sentence[100];
int grade;
scanf(….);
printf("%s %d", sentence, grade);
}
Input:
My CS Grade is 1000
Output:
My CS Grade is 100
However, the kicker is that I need the scanf to read a c-string and then an int with a single scanf command, is this even possible?
Edit:
I can only edit the code in the location with the three periods ( "..." ), I cannot use anything more. I can assume that the input listed is expected but I cannot change anything outside of the three periods.
The output does not contain typos, the purpose of this assignment is to use flags and escape sequences.
It is possible to read pre-formatted string using scanf, however the format must be strict.
This version will continue to read the input until a digit is encountered and then read an integer.
Here is your code again:
char sentence[100];
int grade;
scanf("%[^0-9] %d",sentence,&grade);
printf("%s %d\n", sentence, grade);
I'll get this over with quick:
<obligatory_rant>
stupid question, but I guess it's homework and you're
stuck with these absurd limitations
</obligatory_rant>
Then, if you need to read everything up to but excluding the first digit, then the number:
if (scanf("%100[^0-9] %3d", text, &number) == 2)
...
Notes:
100 in "%100[... should be whatever your actual buffer size is to protect against buffer overrun.
The %3d documents that at most 3 digits should partake the the numeric value, so 1000 is correctly read as 100.
[^...] means the string made up of characters not ("^") in the following set, which is then specified as 0-9 - the digits.
if (... == 2) tests whether both positional parameters were scanned / converted successfully.
If you can't add an if and error message, then simply:
scanf("%100[^0-9] %3d", text, &number)
Tested in Visual Studio 2008
#include <stdio.h>
int main()
{
char sentence[100];
int grade = 0;
scanf("%[^0-9] %d",sentence,&grade);
printf("%s %d", sentence, grade);
return 1;
}
Input :
My CS Grade is 100
Output :
My CS Grade is 100
This is a really horrible question. A correct set of scanf parameters would be "%14c%3d", sentence, &grade
Because a space is included in the printf statement the trailing space needs to not be stored in sentence. Because the input contains other spaces there is no other solution (that I can thing of) than a fixed length. The integer parsing also requires a fixed length to truncate 1000 to 100.
I can think of no reason to ever write code anything like this. The code fits the requirements but wouldn't be useful in any other circumstances. I think that this is a very poor training exercise.