The If Statement

Loadand display the fileifelse.cfor an example of our first conditional branching statement, the "if".

/* This is an example of the if and if-else statements */
main()
{
int data;
for(data = 0;data < 10;data = data + 1) {
if (data == 2)
printf("Data is now equal to %d\n",data);
if (data < 5)
printf("Data is now %d, which is less than 5\n",data);
else
printf("Data is now %d, which is greater than 4\n",data);
} /* end of for loop */
}

Notice first, that there is a "for" loop with a compound statement as its executable part containing two "if" statements. This is an example of how statement can be nested. It should be clear to you that each of the "if" statements will be executed 10 times.

Consider the first "if" statement. It starts with the keyword "if" followed by an expression in parentheses. If the expression is evaluated and found to be true, the single statement following the "if" is executed. If false, the following statement is skipped. Here too, the single statement can be replaced by a compound statement composed of several statements bounded by braces. The expression "data" == 2" is simply asking if the value of data is equal to 2, this will be explained in detail in the next chapter. (Simply suffice for now that if "data = 2" were used in this context, it would mean a completely different thing.)

The second "if" is similar to the first, with the addition of a new reserved word, the "else",
following the first printf statement. This simply says that, if the expression in the parentheses evaluates as true, the first expression is executed, otherwise the expression following the "else" is executed. Thus, one of the two expressions will always be executed, whereas in the first example the single expression was either executed or skipped. Both will find many uses in your C programming efforts. Compile and run this program to see if it does what you expect.