I have started working on the project below here. I want to practice my C coding skills. I would love any constructive criticism I can get!

It is a grading program: given a set of subject marks, it converts to an alphabetic grade letter.

#include <stdio.h>

#include <stdlib.h>

int main()

{

    char name[100];

    int physics,chemistry,maths,biology,business,total_marks;

    // physics,chemistry,maths,biology,business are just but subjects names.

    float mean;

     printf("Please enter your name n");

     fgets(name,100,stdin);

     {

    printf("Please enter the marks for physics n");

    scanf("%d",&physics);

    printf("Please enter the marks for chemistry n");

    scanf("%d",&chemistry);

    printf("Please enter the marks for maths n");

    scanf("%d",&maths);

    printf("Please enter the marks for biology n");

     scanf("%d",&biology);

    printf("Please enter the marks for businessn");

     scanf("%d",&business);

     total_marks=physics+chemistry+maths+biology+business;

     mean= (float)total_marks/5;}

printf("%st",name);

printf(" HAS TOTAL MARKS OF : %d,t",total_marks);

printf(" MEAN OF :  %.2ft",mean, round(mean) );

if (mean>=70)

    printf("AND THE  GRADE IS A  n");

if(mean>=60 && mean<69)

    printf("AND THE  GRADE IS B  n");

if(mean>=50 && mean<59)

    printf("AND THE  GRADE IS C  n");

if(mean>=40 && mean<49)

    printf("AND THE  GRADE IS D  n");

    if (mean<40)

    printf("AND THE  GRADE IS E n");

    printf(" Thank you for your time  n");

    return 0;

}

The first thing you should do is to let your editor or your IDE format the source code. Right now it looks confusing because the lines are not properly indented. I ran GNU Indent with the -kr option on your code:

indent -kr marks.c

This is the result:

#include <stdio.h>

#include <stdlib.h>

int main()

{

    char name[100];

    int physics, chemistry, maths, biology, business, total_marks;

    // physics,chemistry,maths,biology,business are just but subjects names.

    float mean;

    printf("Please enter your name n");

    fgets(name, 100, stdin);

    {

        printf("Please enter the marks for physics n");

        scanf("%d", &physics);

        printf("Please enter the marks for chemistry n");

        scanf("%d", &chemistry);

        printf("Please enter the marks for maths n");

        scanf("%d", &maths);

        printf("Please enter the marks for biology n");

        scanf("%d", &biology);

        printf("Please enter the marks for businessn");

        scanf("%d", &business);

        total_marks = physics + chemistry + maths + biology + business;

        mean = (float) total_marks / 5;

    }

    printf("%st", name);

    printf(" HAS TOTAL MARKS OF : %d,t", total_marks);

    printf(" MEAN OF :  %.2ft", mean, round(mean));

    if (mean >= 70)

        printf("AND THE  GRADE IS A  n");

    if (mean >= 60 && mean < 69)

        printf("AND THE  GRADE IS B  n");

    if (mean >= 50 && mean < 59)

        printf("AND THE  GRADE IS C  n");

    if (mean >= 40 && mean < 49)

        printf("AND THE  GRADE IS D  n");

    if (mean < 40)

        printf("AND THE  GRADE IS E n");

    printf(" Thank you for your time  n");

    return 0;

}

Now the code structure is a little clearer than before.

The next thing I noticed is that your code does not have a single empty line. This always feels to me as if youwerewritingyourcodewithoutanyspaces, and this also makes it unnecessarily hard to see the building blocks of the code. I added the empty lines manually since I don't know any program that could automatically do this. Now your code is:

#include <stdio.h>

#include <stdlib.h>



int main()

{

    char name[100];

    int physics, chemistry, maths, biology, business, total_marks;

    // physics,chemistry,maths,biology,business are just but subjects names.

    float mean;



    printf("Please enter your name n");

    fgets(name, 100, stdin);



    printf("Please enter the marks for physics n");

    scanf("%d", &physics);

    printf("Please enter the marks for chemistry n");

    scanf("%d", &chemistry);

    printf("Please enter the marks for maths n");

    scanf("%d", &maths);

    printf("Please enter the marks for biology n");

    scanf("%d", &biology);

    printf("Please enter the marks for businessn");

    scanf("%d", &business);



    total_marks = physics + chemistry + maths + biology + business;

    mean = (float) total_marks / 5;



    printf("%st", name);

    printf(" HAS TOTAL MARKS OF : %d,t", total_marks);

    printf(" MEAN OF :  %.2ft", mean, round(mean));



    if (mean >= 70)

        printf("AND THE  GRADE IS A  n");

    if (mean >= 60 && mean < 69)

        printf("AND THE  GRADE IS B  n");

    if (mean >= 50 && mean < 59)

        printf("AND THE  GRADE IS C  n");

    if (mean >= 40 && mean < 49)

        printf("AND THE  GRADE IS D  n");

    if (mean < 40)

        printf("AND THE  GRADE IS E n");



    printf(" Thank you for your time  n");

    return 0;

}

At this stage the code is ready to be read by a human. Before it just looked like a mess.

One thing I already did in the previous step is to remove the { and } around the subjects input block. They didn't serve any purpose.

In the first block of the main function, you only declare variables but don't use them. This is dangerous since in C it is a silent error to declare a variable, not initialize it and then read its value. This leads to undefined behavior. Therefore it's better to combine the variable declaration with its first assignment. Instead of this:

float mean;

// ... some 20 lines of unrelated code ...

mean = (float) sum / n;

Better combine these lines:

float mean = (float) sum / n;

In the 1990s, only the first variant of the code was allowed. But that time has long since passed, and there's no reason anymore to declare variables at the top of the function. Instead, declare them right when they are needed.

The strings you print typically end in " n". There's no point in writing a trailing space character before a line break. It won't be visible anyway, so you can simply write "n" instead. Even worse, after business you didn't add a space. Whatever you do in programming, be consistent. Either write the spaces nowhere or everywhere. In this case nowhere.

WHY DO YOU MAKE YOUR PROGRAM SHOUT SO LOUD? There's no reason to use all-uppercase text in your program. It hurts both the ears and the eyes of the readers of the code.

The round function is only guaranteed to be available in your program if you #include <math.h> at the top.

There's a bug in the program. When the mean grade is 69, it is neither >= 70 nor < 69, therefore none of the result sentences is printed. Instead of the if-then you should use if-then-else-if-then-else-if-else instead:

if (mean >= 70)

    printf("AND THE  GRADE IS A  n");

else if (mean >= 60)

    printf("AND THE  GRADE IS B  n");

else if (mean >= 50)

    printf("AND THE  GRADE IS C  n");

else if (mean >= 40)

    printf("AND THE  GRADE IS D  n");

else

    printf("AND THE  GRADE IS E n");

This is much clearer and is guaranteed to cover all cases. Again, you have trailing spaces here. Just remove them. What does the double space between THE GRADE mean? If there's no meaning to it, just use a single space.

One last point is the error handling. Whenever you call a function like fgets or scanf, you must check its return value, like this:

if (fgets(name, 100, stdin) == NULL)

    return 0;

This can happen if the user presses Ctrl+D (on Linux, macOS or any other UNIX-like operating system) or Ctrl+Z (on Windows) and thereby terminates the input. For scanf this error checking is even more important. What if the user enters dgfhtzhrdghfnjfthfd instead of a number? Therefore:

if (scanf("%d", &physics) != 1) {

    fprintf(stderr, "error: physics mark must be a numbern");

    return EXIT_FAILURE;

}

That's all for now.

Formatting - if the code looks the same in your editor as it does here, you could really do with an automatic indentation tool (many editors have that built-in, or you could use GNU Indent, for instance).

I'll assume that the inconsistent indentation is due to the way you've copied your code into the site; a good way to avoid problems is to consistently use either spaces or tabs for indentation, but never to mix the two.

It's a good idea to specify that main() takes no arguments:

int main(void)

When we read input, we must check whether it was successful or not:

int physics;

if (scanf("%d", &physics) == 1) {

   // physics has been set, and we can safely use it

} else {

   // physics is still uninitialised

}

If input fails, then we might want to re-ask (but be careful about doing this if we reach end of the input stream, or we'll try and try again, indefinitely).

Output can also fail, but for this application, that's less of a concern.

There's an unused argument to printf() here:

printf(" MEAN OF :  %.2ft",mean, round(mean) );

That suggests that you could enable more compiler warnings (e.g. gcc -Wall -Wextra - other compilers should have similar options).

If mean is between (say) 59.0 and 60.0, then it will fall in between the grade boundaries, and no grade will be printed. The easy way to avoid this is to use else if:

if (mean >= 70) {

    puts("AND THE  GRADE IS A");

} else if (mean >= 60) {

    puts("AND THE  GRADE IS B");

} else if (mean >= 50) {

    puts("AND THE  GRADE IS C");

} else if (mean >= 40) {

    puts("AND THE  GRADE IS D");

} else {

    puts("AND THE  GRADE IS E");

}

Now, exactly one of those blocks will be executed.

I also changed the printf() to puts() there - prefer the simpler function when you just need to print a single string and a newline.

More advanced ideas

Should the grade thresholds be fixed in the code? If they change, you need to re-compile the program. Think about how you might read them from a configuration file.

Should the list of subjects be fixed? How would you make the program more flexible for students of different courses?