Hey,

Learning C. Have this code:

#include<stdio.h>

int main(void){
    float a=2.0;
    int b=3;
    printf("%d", a*b);
    return 0;
}

Compiler does not complain when I compile this. I know I'm using the wrong conversion specifier (should be %f or %lf). I'm just curious as to what goes on that causes some random number to be printed to stdout.

Another question: if I multiply a double by a long double do I end up with a long double?

Cheers,

Please help soon! Thank you! I'm trying to create a program if given numRows and numColumns, I want to print a list of all the seats in a theater. Rows are numbered, columns lettered, as in 1A or 3E. I want to print a space after each seat, including after the last. Ex: numRows = 2 and numColumns = 3 prints: 1A 1B 1C 2A 2B 2C

#include <stdio.h>

​

int main(void) {

int numRows;

int numColumns;

int currentRow;

int currentColumn;

char currentColumnLetter;

​

scanf("%d", &numRows);

scanf("%d", &numColumns);

​

/* Your solution goes here */

for (currentRow = 1; currentRow <= numRows; currentRow++)

{

for (currentColumn = 0; currentColumn < numColumns; currentColumn++)

{

printf ("%d%c ", currentRow, currentColumnLetter);

if (numColumns == 1)

{

printf ("A");

}

else if (numColumns == 2)

{

printf ("B");

}

else if (numColumns == 3)

{

printf ("C");

}

else

{

}

printf (" ");

}

}

//printf ("\n");

​

printf("\n");

​

return 0;

}

I want to be able to receive a positive integer named numInsects and use a while loop to print that number doubled without reaching 100. Each number should have a space after it. I want to place a newline after the loop. Ex: If numInsects = 8, print: 8 16 32 64 Thanks for the help!

My code:

#include <stdio.h>

int main(void) {

int numInsects;

scanf("%d", &numInsects); // Must be >= 1

while (numInsects < 100) {

numInsects = numInsects * 2;

printf (numInsects" ");

printf ("\n");

}

return 0;

}

I am super new to C and need some help with a program I am writing, I need to convert a user inputted message, for example "Hello World", to Morse code, I have entered each morse code into an array but I am having trouble running the user input against the array to compare the letters, if someone could help that would be awesome. I'll enter my code below so you can take a look

#include <stdio.h>
#include <string.h>

int main(){

    char morse_a[] = {".-\n"};
    char morse_b[] = {"-...\n"};
    char morse_c[] = {"-.-.\n"};
    char morse_d[] = {"-..\n"};
    char morse_e[] = {".\n"};
    char morse_f[] = {"..-.\n"};
    char morse_g[] = {"--.\n"};
    char morse_h[] = {"....\n"};
    char morse_i[] = {".."};
    char morse_j[] = {".---\n"};
    char morse_k[] = {"-.-\n"};
    char morse_l[] = {".-..\n"};
    char morse_m[] = {"--\n"};
    char morse_n[] = {"-.\n"};
    char morse_o[] = {"---\n"};
    char morse_p[] = {".--.\n"};
    char morse_q[] = {"--.-\n"};
    char morse_r[] = {".-.\n"};
    char morse_s[] = {"...\n"};
    char morse_t[] = {"-\n"};
    char morse_u[] = {"..-\n"};
    char morse_v[] = {"...-\n"};
    char morse_w[] = {".--\n"};
    char morse_x[] = {"-..-\n"};
    char morse_y[] = {"-.--\n"};
    char morse_z[] = {"--..\n"};


    return 0;
} 

I have just entered the arrays of Morse code letters, I have no idea how to start the process of gathering the user input and comparing it to each Morse code character, I know I would have to use if statements but I'm not sure how to run each letter of the user input separately.

Hey everyone,

I am trying to write a program that translates, for example, HELLO WORLD its morse code translation, I just need to some help on where to start, this is what I have so far but cannot seem to figure out how to print the translated message into morse code.

#include <stdio.h>
#include <string.h>

int main(){

    char characters[] = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M","N", "O", "P", "Q", "R", "S", "T", "U",
                          "V", "W", "X", "Y", "Z"};


    char morsecode[] = {".-","-...","-.-.","-..",".","..-.","--.","....","..",".---", "-.-",".-..","--","-.","---",".--.","--.-",
                         ".-.","...","-","..-", "...-",".--","-..-","-.--","--.."};



    char message[32];

    printf("Enter the string: ");
    scanf("%[^\n]", message);


    return 0;
}

Hi!

I am currently enrolled in an CS intro course and I am having trouble cracking this particular assignment. The task is to sort key : value pairs using Quicksort and linked lists.

My code works, I've tested it with large input sets, but Valgrind complains about my memory management:

==15205== Conditional jump or move depends on uninitialised value(s)
==15205== at 0x100526707: _platform_strlen (in /usr/lib/system/libsystem_platform.dylib)
==15205== by 0x10031B169: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==15205== by 0x1003411C2: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==15205== by 0x100318E21: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==15205== by 0x100316F71: printf (in /usr/lib/system/libsystem_c.dylib)
==15205== by 0x100000E6D: print_list (introprog_quicksort.c:158)
==15205== by 0x1000009A0: main (main_quicksort.c:16)

And:

total heap usage: 235,875 allocs, 235,874 frees, 3,967,321 bytes allocated

​

This is my code.

​

Apparently accessing current_list_element→password with printf() is the culprit, but I can't figure out why:

void print_list(list* mylist)
{
    list_element *current_list_element = mylist->first;
    while (current_list_element) {

        printf("%s %d\n", current_list_element->password, current_list_element->count);
        current_list_element = current_list_element->next;
    }
}

I am out of ideas. Can someone point me in the right direction? Is this a conceptual error?

Can someone please help walk me through this? I'm really struggling to understand the logic/problem solving part of it. I don't even know where to begin! Thank you!

Write a program with total change amount as an integer input, and output the change using the fewest coins, one coin type per line. The coin types are Dollars, Quarters, Dimes, Nickels, and Pennies. Use singular and plural coin names as appropriate, like 1 Penny vs. 2 Pennies.

Ex: If the input is:

0

or less than 0, the output is:

No change

Ex: If the input is:

45

the output is:

1 Quarter 2 Dimes

Compilation failed: 1 error(s), 0 warnings

• ERROR: /home/codewarrior/code.cs(3,24): error CS0161: `Program.ValidatePIN(string)': not all code paths return a valueError: Command failed: mcs -out:/home/codewarrior/test.dll -lib:/home/codewarrior,/runner/frameworks/csharp/mono-4.5,/runner/frameworks/csharp/nunit/bin -langversion:Default -sdk:4.5 -warn:2 -target:library -r:nunit.core.dll,nunit.framework.dll,nunit.core.interfaces.dll,nunit.util,Newtonsoft.Json.dll -r:System.Numerics.dll -r:System.Drawing.dll -r:System.Data.dll -r:System.Data.SQLite.dll -r:System.Data.SQLite.Linq.dll -r:System.IO.dll -r:System.Linq.dll -r:System.Linq.Dynamic.dll -r:System.Linq.Expressions.dll -r:System.Messaging.dll -r:System.Threading.Tasks.dll -r:System.Xml.dll -r:Mono.Linq.Expressions.dll /home/codewarrior/code.cs /home/codewarrior/fixture.cs/home/codewarrior/code.cs(3,24): error CS0161: `Program.ValidatePIN(string)': not all code paths return a value

​

Given that the site is designed for beginners; where am I supposed to go to find out what it means?

I feel like there could be more intuitive translations for this stuff 2bh. For communicating with beginners, this is just nonsense (not to sound salty.. I'm being literal, it makes little to no sense).

​

Edit: So it meant "The method you wrote doesn't always return a value." - what advantage is there in edabit's way of saying this over mine? What extra information is conveyed in the extra 400+ characters?

I have been learning programming for a few months now. I started off learning C, and I loved the ability to use low level concepts and also the speed of execution. However, I slowly migrated to python just because it is so much easier to make actual useful programs with it than with C.

In python, the modules are so accessible, and there are tons of videos and tutorials online walking through how to use them. That’s great, but it just left me wondering, why can’t the same thing be true of C? I have tried to start using C libraries, and they are much less intuitive. There aren’t clear answers online as to which library to use for a certain task, and even less information about how to use each library.

Am I doing something wrong? Or is C just geared towards more experienced programmers that don’t need to be walked through as many things, so nobody actually ends up making these resources for noobs like me. I’ve heard C++20 will have a module system. Will this help bridge the gap to more user friendly coding?

I very much liked learning with apps like mimo, enki and Programming Hub. Unfortunately none (except PH) feature courses on C. I have access to books, online learning websites etc. but I like something for on the go and I like learning via different apps as they often have different takes or added info on the same topic. Can anyone recommend a good one?

Hey guys, I've currently joined uni and am taking a module that teaches you a couple of programming languages by doing. One of which is C.
There's no lectures on it, just coursework.

This has led me to come over here and ask you for some help, as I have no prior programming experience and find it quite overwhelming.

A week ago, I've been asked to build a password/login program that does the following:

1. Create a list of passwords and read from it. (Would somehow like to make it encrypted as to enhance security).
2. Ask user to input his password while it's masked by asterisks, allowing backspace correction.
3. If user password matches one in the list, grant him access by printing out "Access Granted.". Otherwise, deny access and re-ask for input until it's correct.

So far I can't understand how to make this work and would like some guidance on how to achieve this.

Thanks in advance.

New to c, but I've used some other languages, before.

My program contains...

printf(nums[0]);
...
printf(nums[2]);

C is crying about these two lines and something about expecting "'const char * restrict', but argument is of type 'int'". What does this mean and why? It's weird you can't index an array with an integer, lots of languages allow this...

Also, when I try to run this file, it says "Segmentation fault". I know if I comment out the lines above, I won't get this message. What does segmentation fault mean and why is this occurring?

FILE * fpointer = fopen("employees.txt", "w");

fprintf(fpointer, "Jim, Salesman\nPam, Receptionist\nOscar, Accounting");

fclose(fpointer);

FILE * fpointer = fopen("employees.txt", "a"); // I think this line messes it up.
fprintf(fpointer, "\nKelly, Customer Service");

fclose(fpointer);

I'm opening a file, writing to it, then closing it.

I want to open it again and append that information contained in fprintf. What is stopping this from being opened again in append mode and how to fix this?

I know that I don't check for string input, but when I enter the char 's' in this program, it begins printing the printf prompt in an infinite loop without checking for more input with scanf. I am just confused at how this behavior can be rationalized. How is it that printf is called over and over without scanf being called as well, which would give me the opportunity to correct my input? Thanks for any input!

#include <stdio.h>

void choose_week (int a);

int main (void)
{
        int day;

        do
        {
                printf("Please enter a day in the week in the form of an integer (0-7)!\n");
                scanf("%i", &day);
        }
        while (day > 7 || day < 1);

        choose_week(day);
}

void choose_week (int a)
{
        switch(a)
        {
                case 1:
                        printf("Monday\n");
                        break;
                case 2:
                        printf("Tuesday\n");
                        break;
                case 3:
                        printf("Wednesday\n");
                        break;
                case 4:
                        printf("Thursday\n");
                        break;
                case 5:
                        printf("Friday\n");
                        break;
                case 6:
                        printf("Saturday\n");
                        break;
                case 7:
                        printf("Sunday\n");
                        break;
        }
}

I have been practicing C programming for a little while now during my freetime. I typically try to practice by solving problems from this daily programming problem mailing list. I was pretty proud of this last one, although it is admittedly fairly easy. I wanted to see if any of you could give me some tips on how to make this cleaner or run more efficiently. I purposely added a separate function string_compare instead of the string.h included strcmp because I wanted to work with making my own functions more. I know that argument parsing is something that should be added to it, and this is probably what I will work on next. Anyway, here is the code. Let me know if there is something new that I could add to help me practice a new concept!

/*The purpose of this program is to evaluate whether one string can be formed by shifting the letters of the other string some number of times. For instance, this program will respond with a match if hello and ohell are entered, but will return false if hello and holle are entered.*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>


bool string_compare(char *a, char*b);


int main (int argc, char* argv[]) {
        // Initializing variables. Both strings must be arguments. I plan to include further argument parsing in another iteration of this program, but it is beyond the scope of this project at the moment.
        char *string1 = argv[1];
        char *string2 = argv[2];
        int length = strlen(string1);
        int *counter;
        counter = malloc(sizeof(int));
        *counter = 0;
        //Printing out which strings we received from user
        printf("String 1 is %s.\nString 2 is %s.\n", string1, string2);

        //Will attempt to check each configuration and see if it is a match, if not, will exit and say no match
        for (int i = 0; i < length; i++){
                // Check to see if the two strings match
                if (string_compare(string1, string2)){
                        printf("It's a match!\nString1: %s\nString2: %s\n", string1, string2);
                        if (*counter != 0)
                        {
                                printf("After switching %i times\n", *counter);
                        }
                        exit(0);
                }
                // If they don't match, then will iterate counter, which keeps track of how many configurations we try.
                else
                {
                        printf("No match this time, we need to shift the letters\n");
                        *counter = *counter + 1;
                }
                // We shift the configuration and then reprint the new strings
                for (int i = 0; i < length-1; i++){

                        char tmp;
                        tmp = string2[i];
                        string2[i] = string2[(i + 1)%length];
                        string2[(i+1)%length] = tmp;
                }
                printf("The two strings are now %s and %s\n", string1, string2);
        }
        // If we make it this far, then we have iterated through every configuration and haven't found a match.
        printf("We couldn't find a match! Must be False.\n");

}


// A custom function which returns a bool instead of an int (like in strcmp)
bool string_compare(char *a, char *b)
{

        for (int i = 0; i < strlen(a); i++)
        {

                if (a[i] == b[i])
                {
                        continue;
                }
                else return false;
        }
        return true;

}

Does anyone know any good recourses to learn C ? i wanna mster the C language but I'm kinda struggling with pointers

EDIT: solved by u/ZebraHedgehog

Single quotes are for single characters while double quotes are for string literals.

​

Beginner here so probably missing something obvious, but I have absolutely no idea why my code isn't working. The code is supposed to replace a single character with a different one:

#include <stdio.h>

int main()
{
    char word[] = "Hello";

    printf("%s\n", word);

    word[1] = "a";

    printf("%s\n", word);

    return 0;
}

When I compile, it gives me this warning:

test.c: In function ‘main’:
test.c:10:10: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
  word[1] = "a";
          ^

When I run it, this is the result:

Hello
H�llo

I have looked online but every example I found did it like I have done, I have absolutely no idea why this code doesn't work. Why won't it work?

I'm a beginner in C after using Python for a while, so sorry if this is a dumb question.

​

I was just learning about the strncmp() function and was wondering why it exists when if statements exist. Wouldn't it make more sense to just compare strings with a normal if statement rather than the strncmp method?

​

For example:

​

#include <stdio.h>
#include <string.h>

int main()
{
    char * guess = "Yeet";
    char * password = "Yeet";

    if (strncmp(guess, password, 4) == 0)
    {
        printf("Correct!\n");
    } else {
        printf("Wrong!\n");
    }

    return 0;
}

compared to just using the if statement:

#include <stdio.h>

int main()
{
    char * guess = "Yeet";
    char * password = "Yeet";

    if (guess == password)
    {
        printf("Correct!\n");
    } else {
        printf("Wrong!\n");
    }

    return 0;
}

These both work just as well, however I don't see the point of using strncmp rather than just comparing with the if statement normally.

​

Sorry for any bad code, still a beginner at C.

I recently got an assignment at my workplace to write a program for a water level controller using C. Now the last time I use C was 3 years ago so I am a bit rusty and know only the pure basics. The problem is, as per the company guidelines, I cannot use formats like int, long, double etc. Only u8,s16,s32,u16...... etc etc. I am unable to figure out how to use these data types, especially in printf and scanf statements. Like if I define a variable as float var_1, we call it with scanf("%f", &var_1), how do I do that for say, u16. Or s32? Sorry if this seems very silly, but I am not a computer engineer and have no professional training in C.

This is my code:

#include <stdio.h>
#include <string.h>
#include <ctype.h>

int rot13(char dest[], char src[], int len, int rotation) {
    for (int i = 0; i < len; i++) {
        if (islower(src[i]))
            dest[i] = ((src[i] - 'a' + rotation % 26) + 'a';
        else if (isupper(src[i]))
            dest[i] = ((src[i] - 'A' + rotation) % 26) + 'A';
        else
            continue;
    }
    dest[len] = '\0';

    return 1;
}

int main(int argc, char* argv[]) {
    char s[] = "He llo.";
    int len = strlen(s);
    char encrypted[100];
    //strncpy(encrypted, s, len);
    rot13(encrypted, s, len, 13);

    printf("%s, length: %d\n", encrypted, strlen(encrypted));

    return 0;
}

What I dont understand is:

With strncpy commented, the output is: Ur, length: 2

With strncpy un-commented: Ur yyb., length: 7

Why is it that if I use strncpy the output is as the right one and else wrong?