A Very Short Intro to C

Clément Aubert

septembre 5, 2018

Installation, Compilation and Execution

You can find at http://spots.augusta.edu/caubert/teaching/general/C/prog.c and below a simple C program:

/*
 * I'm a comment.
 */

#include <stdio.h> // To perform input / output, printf and scanf
#include <stdlib.h> // To add EXIT_SUCCESS and EXIT_FAILURE, cf end of the main method.

long cube(long x){
    return x * x * x;
}

int main(){
    int a;
    a = 10;
    int b = 11;
    
    printf("The value of a is %d, its address is %p\n", a, &a);
    //%d is for sigmed integers, %p for pointer address
    
    int* pointer = &a;
    // You can also see the syntax "int *pointer = &a;".
    printf("The value pointed is %d, the address of the pointer is %p, the address the pointer points to is %p.\n", *pointer, &pointer, pointer);
    
    // Notice that if the value of change a, so does the value pointed at. We can read the new value from the user:
    printf("Enter the new value for a and press enter:\n");
    scanf("%d", &a);
    printf("The value pointed is %d\n", *pointer);

    // Basic control stucture:
    if (a == 10){
        printf("You did not changed the value of a.\n");
        }
    else
        {
        printf("You changed the value of a.\n");
        }
    
    int counter;
    
    printf("Let's count to ten:\n");
    for (counter = 0; counter <= 10 ; counter++)
        {
        printf("%d ", counter);
        }
    printf("\n");

    printf("Let's count back to 0:\n");
    while (counter > 0)
        {
        counter--;
        printf("%d ", counter);
        }
    printf("\n");

    // Calling the previously defined cube function, performing implicit casting from int to long:
    printf("Here is your number, cubed: %d\n", cube(a));

    /* To exit informing the environment that our program completed successfully, we can use:
     *    return(0);
     *    exit(0);
     * or, more portable:
     */
     exit(EXIT_SUCCESS);
}

You can find services to compile C code online, but I recommend you install gcc or another C compiler on your computer or virtual machine.

To compile and execute it, use

gcc prog.c
./a.out

If you have questions, feel free to reach me at .

Presentation of the Program

This is a really straightforward program in C, hopefully allowing you to get familiar with this programming language.

Among the things that may confuse you:

Pushing Further

There are two excellent textbooks that I recommend:

Playing with the code won’t hurt, and here are some suggestions of exercises:

void plus(int a){
    a = a+1;
    printf("The parameter is now %d", a);
}

and

void plus(int* p){
    *p = *p+1;
    printf("The parameter is now %d", *p);
}