C Syntax, Output and Comments

This chapter explains the parts of a C program and shows how to print output.

The Parts of a C Program

Example

#include <stdio.h>

int main(void) {
  printf("Hello World\n");
  return 0;
}

The example explained

Line	Meaning
`#include <stdio.h>`	Adds the standard input/output library, which contains `printf`
`int main(void)`	The main function, where the program starts. It returns an `int`
`{ }`	Curly braces hold the body of the function
`printf(...)`	Prints text on the screen
`;`	Every statement ends with a semicolon
`return 0;`	Ends main and tells the system the program finished without errors

C ignores extra spaces and blank lines, so use them to keep your code neat.

Printing with printf

printf does not add a new line by itself. Use \n where you want a line break:

Example

#include <stdio.h>

int main(void) {
  printf("Workownix ");
  printf("Institute\n");
  printf("Orangi Town\nKarachi\n");
  return 0;
}

Output

Workownix Institute
Orangi Town
Karachi

Escape Sequences

Code	Result
`\n`	New line
`\t`	Tab space
`\\`	A backslash
`\"`	A double quote

Example

#include <stdio.h>

int main(void) {
  printf("Item\tPrice\n");
  printf("Tea\t120\n");
  printf("He said \"Shukriya\"\n");
  return 0;
}

Output

Item	Price
Tea	120
He said "Shukriya"

Printing Numbers

To print a value, put a format specifier in the text and the value after a comma:

Example

printf("Age: %d\n", 21);
printf("%d + %d = %d\n", 4, 5, 4 + 5);

Output

Age: 21
4 + 5 = 9

Spaces and Lines

C does not care about extra spaces or line breaks between statements. These two programs do the same thing, but the second one is much easier to read:

Example

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

Example

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

Indent the code inside braces by two or four spaces, and keep one statement on each line.

Comments

Comments are notes for humans. The compiler ignores them.

Example

#include <stdio.h>

int main(void) {
  // A single-line comment
  printf("Line one\n");

  /* A comment that
     spans many lines */
  printf("Line two\n"); /* can also go at the end */
  return 0;
}

Output

Line one
Line two

C is case sensitive. printf works, but Printf or PRINTF gives an error.

Exercise

Which escape sequence moves the output to a new line?

\t\n\\/n