4.1. Branching

Branching is so called because the program chooses to follow one branch or another. The if statement is the most simple of the branching statements. It takes an expression in parenthesis and an statement or block of statements (surrounded by curly braces). if the expression is true (evaluates to non-zero) then the statement or block of statements gets executed. Otherwise these statements are skipped. if statements take the following form:

if (expression)
  statement;
     

if (expression)
  {
    statement1;
    statement2;
    statement3;
  }
     

Here's a quick code example:

#include <stdio.h>

int
main()
{
  int cows = 6;

  if (cows > 1)
    printf("We have cows\n");

  if (cows > 10)
    printf("loads of them!\n");

  return 0;
}
    

ciaran@pooh:~/book$ gcc -Wall -Werror -o cows using_if.c
ciaran@pooh:~/book$ ./cows
We have cows
ciaran@pooh:~/book$
    

The second printf() statement does not get executed because it's expression is false (evaluates to zero).