Imperative programming organizes a program as orders for a computer to carry out. A small C program makes the idea visible: it declares an array, repeatedly computes each element's square, and prints the results. section 1.0 section 1.1
Listing 1.1. A first example of a C program
1 /* This may look like nonsense, but really is -*- mode: C -*- */
2 #include <stdlib.h>
3 #include <stdio.h>
4
5 /* The main thing that this program does. */
6 int main(void) {
7 // Declarations
8 double A[5] = {
9 [0] = 9.0,
10 [1] = 2.9,
11 [4] = 3.E+25,
12 [3] = .00007,
13 };
14
15 // Doing some work
16 for (size_t i = 0; i < 5; ++i) {
17 printf("element %zu is %g, \tits square is %g\n",
18 i,
19 A[i],
20 A[i]*A[i]);
21 }
22
23 return EXIT_SUCCESS;
24 }
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Inspect the complete C example: declarations establish the data, the for statement performs repeated work, and printf produces terminal output. section 1.0
The example proceeds through explicit statements. A for loop visits five positions; each iteration passes the index, the selected array value, and its square to printf. The program therefore expresses its task as a sequence of commands rather than an abstract description of the desired result. section 1.1
TAKEAWAY
- C is an imperative programming language. section 1.1
- Statements act as instructions, including calls to functions such as printf. section 1.1
Observable result
Running the program prints five terminal lines, including “element 0 is 9, its square is 81” and “element 4 is 3e+25, its square is 9e+50.” section 1.1
