Printing

printf Function

As you’ve seen, the printf function is used to display output in C. For example, to display a string of text:

printf("Hello\n");

Note that you always need to specify the newline character (\n). There is no println equivalent in C.

Printing Variables

Printing variables works a bit differently. First, you specify the kind of variable that’s going to be printed (called a control string). Then, outside the string, you give the corresponding variable name.

Here are the different control strings:

It’s easiest to see an example to figure out how printing works. Here’s how to print the value of an integer to the screen:

int num = 4;
printf("The value of num is %d\n", num);

Notice that where we want to print a variable, we put the control string (%d for int). After we’ve listed the entire string, we put the corresponding variable names as the next arguments to printf. The above example will print:

"The value of num is 4" 

to the screen.

We can also print several variables at once:

char letter = 'A';
int val = (int) letter;
printf("The ASCII value of %c is %d\n", letter, val);

This prints:

"The ASCII value of A is 65"

to the screen. Notice that the %c corresponds to the letter argument, and the %d corresponds to the val argument.

Formatting

The printf function also allows you some control over formatting your output. For example, if you want a value to take up exactly 6 spaces (padded with space characters on the left, if necessary), put a 6 between the % and the control string character.

For example:

int num = 4;
printf("The value of num is %6d\n", num);

This will print:

"The value of num is 4" 

to the screen (note the padding on the left of the 4).

You can also only display a certain number of digits for decimal numbers. For example, put a .2 in between the % and the control string character to only display two decimal places.

For example:

double val = 3.14159;
printf("Pi is %.2lf\n", val);

This will display:

"Pi is 3.14" 

You can specify both the width of the output (for example, six spaces) and the number of decimals to display by doing something like this:

double val = 3.14159;
printf("Pi is %6.2lf\n", val);