Page 57 - Programming Microcontrollers in C

42 Chapter 1 Introduction to C

To reverse the data, the program starts by decrementing i so that
s[i], the last entry in the array, is the most significant character in
the number, and it must be placed in the first array location s[0]: .
Likewise, the character in s[0] must be placed in s[i]: and so
forth. The while loop that follows accomplishes this requirement.

EXERCISES

1. Write a program atoi(s[]) that starts with a character string
and converts this string to an int. Assume that the string contains
no sign.
2. Write a program that reads a text file one character at a time and
counts the number of words in the file.

The If/Else Statement
The if/else statement has the general form

if(expression)
statement1;
else
statement2;

If the logical evaluation of the expression that is the argument of the
if is TRUE, statement1 will be executed. After statement1
is executed, program control will pass to the statement following
statement2, and statement2 will not be executed. If the evalu­
ation of statement is FALSE, statement2 will be executed, and
statement1 will be skipped. The else statement is not neces­
sary. If there is no else statement, the expression is evaluated. If it
is TRUE, statement1 will be executed. Otherwise, statement1
will be skipped. The following program demonstrates the use of the
if/else flow control method.

/* count number of digits and other characters in
input */

#include <stdio.h>

int main(void)