Introduction

C can be a very difficut language to learn. From compiling it, to accepting user input, every aspect has a significant learning curve. In this article, we will build a C converter program which takes in a number between 0 and 100 and returns a letter grade.

Creating Our File

Create a file named converter.c.

Imports

To import external libraries, we use the #include directive. In this program, we will use the stdio.h library. This library contains many basic functions, such as printf, scanf, and getchar.

#include <stdio.h>

Main

We will declare our main program with a return type of int. The function will not take in any args so we will use void.

int main(void)
{
    // code will go here!

    return 0;
}

Note the line return 0; at the end of the function. This means the function has finished running successfully. If we changed this to return 1;, that would mean the function would have failed.

Accepting User Input

Now that we have our function, we can begin by getting an int from the user. We will achieve this in two steps.

1. Declare a variable to hold the user's input.
2. Use the scanf function to get the user's input.

int main(void)
{
    int grade; // local variable of type int to store numerical grade

    printf("Enter a numeric grade: "); // prompt user for input
    scanf("%d", &grade); // store input in local variable grade

    return 0;
}

We use %d to tell the scanf function to read in an int and store it in the variable grade. We use &grade to tell the function to store the value of grade in the memory address of grade.

If/Else Statements

Lastly, we will use an if/else statement to determine the letter grade.

if (grade > 100 || grade < 0) printf("Invalid grade.\n");
    else if (grade >= 90) printf("A\n");
    else if (grade >= 80) printf("B\n");
    else if (grade >= 70) printf("C\n");
    else if (grade >= 60) printf("D\n");
    else printf("F\n"); // end if else statement

Complete Program

All together the code looks like this:

#include <stdio.h>

int main(void)
{
    int grade; // local variable of type int to store numerical grade

    printf("Enter a numeric grade: "); // prompt user for input
    scanf("%d", &grade); // store input in local variable grade

    // start if else statement to determine letter grade
    if (grade > 100 || grade < 0) printf("Invalid grade.\n");
    else if (grade >= 90) printf("A\n");
    else if (grade >= 80) printf("B\n");
    else if (grade >= 70) printf("C\n");
    else if (grade >= 60) printf("D\n");
    else printf("F\n"); // end if else statement

    return 0;
}

Compiling

To compile our program, we will use the gcc command.

gcc -o converter converter.c

This will compile our program and allow us to run it by typing ./converter. We are using the -o flag to tell the compiler to output the executable to the file converter instead of the default a.out.

Running

To run our program, we will use the ./converter command.

./converter

If you run the program and pass in a grade of 87, you should see the following output:

Enter a numeric grade: 87
B

Conclusion

In this article, we created a C program which takes in a numerical grade and returns the letter grade. We covered some basic C concepts such as variables, if/else statements, and functions. We also used the gcc command to compile our program. Happy coding!