C Programming Absolute Beginner's Guide (3rd Edition)

The following program segment prints yes or no, depending on the user’s input. Without the
toupper() function, you need an extra test to execute your plan:

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if ((userInput == 'Y') || (userInput == 'y'))

{ printf("yes\n"); }

else

{ printf("no\n"); }

The next set of statements uses the toupper() function to streamline the if statement’s logical test
for lowercase letters:

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if (toupper(userInput) == 'Y') // only need to test for upper case

{ printf("yes\n"); }

else

{ printf("no\n"); }

String Functions

The string.h header file contains descriptions for more functions than just strcpy() and
strlen(). This section explains the strcat() function that lets you merge two character arrays,
as long as the arrays hold strings. strcat() stands for string concatenation.

strcat() takes one string and appends it to—that is, adds it onto the end of—another string. This
code fragment shows what happens with strcat():

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char first[25] = "Katniss";

char last[25] = " Everdeen";

strcat(first, last); //Adds last to the end of first

printf("I am $s\n", first);

Here is the output of this code:

I am Katniss Everdeen

strcat() requires two string arguments. strcat() tacks the second string onto the end of the
first one. The space appears before the last name only because the last array is initialized with a
space before the last name in the second line.

Warning

You are responsible for making sure that the first array is large enough to hold both

strings. If you attempt to concatenate a second string to the end of another string, and

the second string is not defined with enough characters to hold the two strings, strange

and unpredictable results can happen.

Because the second argument for strcat() is not changed, you can use a string literal in place of a
character array for the second argument, if you like.