A number as a condition
for (size_t i = 0; i < 5; ++i) { if (i) { printf("element %zu is %g\n", i, A[i]); } } Here, i is used directly as the controlling expression. The value 0 is false; every nonzero value is true. This makes if (i) equivalent in meaning to if (i != 0) for a numerical value. section 3.1
A scalar is a C value or type representing one non-aggregate value rather than a collection of components. The scalar types used here include signed and unsigned integers, floating-point values, characters, booleans, strings, pointers, and size-related types. section 3.1
Scalar values have two especially practical roles:
- They can control conditional execution: 0 represents logical false, and any value different from 0 represents logical true. section 3.1
- They can be initialized with an expression convertible to the scalar type, optionally surrounded by braces: double a = 7.8; and double d = { 0 }; are valid forms. section 5.5
- The default initializer {0} is valid for every object type that is not a variable-length array. section 5.5
Table 3.1. Scalar types used in this book (view table figure)
| Level |
Name |
Other |
Category |
Where |
printf |
|---|---|---|---|---|---|
| 0 | size_t | Unsigned | <stddef.h> | "%zu" "%zx" | |
| 0 | double | Floating | Built in | "%e" "%f" "%g" "%a" | |
| 0 | signed | int | Signed | Built in | "%d" |
| 0 | unsigned | Unsigned | Built in | "%u" "%x" | |
| 0 | bool | _Bool | Unsigned | <stdbool.h> | "%d" as 0 or 1 |
| 1 | ptrdiff_t | Signed | <stddef.h> | "%td" | |
| 1 | char const* | String | Built in | "%s" | |
| 1 | char | Character | Built in | "%c" | |
| 1 | void* | Pointer | Built in | "%p" | |
| 2 | unsigned char | Unsigned | Built in | "%hhu" "%02hhx" |
Compare the scalar categories, headers, and printf conversions used for common C values. section 3.1
