C Programming For Dummies Cheat Sheet

Most coding starts with a C language structure. This skeleton includes the basic bones upon which most programs are written. Use this simple skeleton to get started:

#include <stdio.h>
int main()
{
    return(0);
}

Traditionally, the program begins with preprocessor directives plus prototypes. The #include statements bring in header files, such as stdio.h, the standard input/output header file.

The primary function in all C code is main(), which is the first function that’s run when the program starts. The main() function is an int function, so it must return an integer value. All the function’s statements are enclosed in curly brackets, or braces.

The C language keywords represent the core of the language. With the C11 revision to the language, several new keywords have been added. They’re shown with leading underscores in the following table:

Keep the following points in mind as you start programming in C:

• Do not name any function or variable the same as a keyword.

• You use only a few of the C language keywords in your code. Some of them, you’ll probably never use.

• Most of the work in your code is done by functions, not by keywords.

• The C library holds the definitions for many functions. These are prototyped in header files.

Rather than make all your variables floating-point values, it’s more efficient to examine the type of data that’s stored and then choose an appropriate C data type.

Type                                       Value                                                                     Range

Keep these C language data type points in mind:

• Ensure that you choose the proper data type for the values you need to store.
• The _Bool type stores only two values, 0 and 1, which can represent TRUE or FALSE or On or Off or any binary condition.
• The char data type stores character values, though it can also be used to store tiny integers.
• Integers, or whole numbers, are stored in the int data types.
• Any type of value, from the very large to the very small, and any fractional values are stored in the float and double
• Remember to use int values for functions that generate integers, such as getchar(). It’s easy to assume that the function returns a char value because of the function’s name.
• C lacks a string data type. Instead, an array of char variables is used.
• Other data types include structures, arrays, and pointers.

When you cannot type characters into your string, use the escape sequences to insert nonprintable characters into text strings, char variables, and arrays. Here are common C escape sequences:

The printf(), scanf() and other functions use conversion characters as placeholders for various values. Conversion characters are used to indicate a value when the function runs in the final program.

Conversion-character formatting

The options available for conversion characters in C are extensive. The printf() man page lists many of them, with some requiring a bit of experimentation to get them correct. Generally speaking, here’s the format for the typical conversion character:

%-pw.dn

Only the first and last characters are required: % is the percent sign that prefixes all conversion characters, and n is the conversion character(s).

– The minus sign; works with the w option to right-justify output.

p The padding character, which is either zero or a space, when the w option is used. The padding character is normally a space, in which case the p need not be specified. When p is 0, however, the value is padded on the left with zeroes to match the width set by the w option.

w The width option; sets the minimum number of positions in which the information is displayed. Output is right-justified unless the – prefix is used. Spaces are padded to the left, unless the p value specifies the character 0 (a zero).

.d The dot, followed by a value, d, that describes how many digits to display after the decimal in a floating-point value. If d isn’t specified, only the whole-number portion of the value appears.

n A conversion character, as shown in the table in this appendix. Or it can be the percent sign (%), in which case a % appears in the output.

The order of precedence determines which operators act upon a value first. When crafting expressions, know the order of precedence to ensure that the program does what you intend.

• The order of precedence goes as shown here and is overridden by using parentheses. C always executes the portion of an equation in parentheses before anything else.
• Incremented or decremented variables as lvalues (assigned to another value) operate left-to-right. So ++var increments before its value is assigned; var++ increments its value after it’s assigned.
• Associativity for the assignment operators moves right-to-left. For example, the operation on the right side of += happens first.
• The order of precedence may also be referred to as the order of operations.