C tutorial, about printf()

This second tutorial is about the use of the printf() function in .c

Contents

Our first test with printf()

When we use the printf() function, we have to add the stdio.h include at the beginning of the file:

#include <stdio.h>

int main()
{
  printf("hello\n");
  return 0;
}

Here we just print a simple text, "hello\n", the char "\n" at the end, is there to add a new-line.

gcc test1.c -o test1.exe
./test1.exe
hello

the line return 0 at the end is there to return an eventual error-code. with 0, it means there was no error. the standard error-code in case there was an error in the program is 1

you can check this return'd code with:

./test1.exe
echo $?
0

in the previous tutorial, we saw some of the basic type's in .c

here is how to print an int:

#include <stdio.h>

int main()
{
  int d;
  d = 3;
  printf("my-int, d: %d\n", d);
  return 0;
}

test'ing:

$ gcc test2.c -o test2.exe
$ ./test2.exe
my-int, d: 3

Text

A string example:

#include <stdio.h>

int main()
{
  char s[] = "alpha";
  printf("hello %s\n", s);
  return 0;
}

testing:

$ gcc test3.c -o test3.exe
$ ./test3.exe
hello alpha

Float's

#include <stdio.h>

int main()
{
  float f = 3.2;
  printf("my-float: %f\n", f);
  return 0;
}

$ gcc test4.c -o test4.exe
$ ./test4.exe
my-float: 3.200000

the standard format for a float is '%f', but as you can see it will print a number of 0 zero's at the end, so we can use '%g' in-stead:

#include <stdio.h>

int main()
{
  float f = 3.2;
  printf("my-float: %g\n", f);
  return 0;
}

$ gcc test4b.c -o test4b.exe
$ ./test4b.exe
my-float: 3.2

Printing a Structure

here we write a print_stc() function

#include <stdio.h>

struct _stc {
  int d1;
  float f2;
  char *s;
};

void
print_stc(struct _stc *stc)
{
  printf("my-stc: {\n");
  printf(" %d\n", stc->d1);
  printf(" %g\n", stc->f2);
  printf(" %s\n", stc->s);
  printf("}\n");
}

int
main()
{
  struct _stc stc = {
    11,
    3.4,
    "hello"
  };
  print_stc(&stc);
  return 0;
}

we provide the address of our struct with &, so the function print_stc() recieves a pointer to the structure, this is why in the prototype of our function there is a '*' char before the name of the var.

as the function recieves a pointer, the field's are access'd with ->.

$ gcc test5.c -o test5.exe
$ ./test5.exe
my-stc: {
 11
 3.4
 hello
}

Conclusion, going further

TODO

Version of this document

2026-01-15.a

License

© 2025 Florent Monnier

You can use this document according to the terms of either one of these licenses:

You can reuse the pieces of code according to the terms of either one of these licenses:

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