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The English word "assert" means to say or claim that something is correct or true (in a logical sense).

A programming assertion is a claim by the programmer that at a certain point in a program, a certain condition should be true.

Usually assertions are interspersed throughout the code at appropriate points.

Here assertions are used as a way to test the behavior of functions.

Here are the modules needed for Booleans and assertions.
#include <stdbool.h> #include <assert.h>

• The module stdbool.h in the C way of implementing Boolean values.
• The module assert.h is the C way of implementing assertions in code.

The C preprocessor expands the following symbols.

• bool expands to _Bool
• false expands to 0
• true expands to 1

So "Boolean" types in C can be interpreted as 0 for false and 1 for true since this is done by the C preprocessor.

The type _Bool is a special C type that has rules for how to convert to/from other types (e.g., in a condition in a if, while, etc.).

Here is the C code.
#include <stdio.h> #include <stdbool.h> #include <assert.h> int main() { bool b0 = false; bool b1 = true; printf("b0 is %d, false is %d.\n",b0,false); printf("b1 is %d, true is %d.\n",b1,true); return 0; }

Here is the output of the C code.
b0 is 0, false is 0. b1 is 1, true is 1.

Here is the C code.
#include <stdio.h> #include <stdbool.h> #include <assert.h> // begin interface /* given an integer value, dsOdd returns true if the integer is odd, and returns false if it is even */ bool isOdd(int x1); // end interface int main() { printf("(begin main)\n"); assert(isOdd(2) == false); assert(isOdd(3) == true); assert(isOdd(4) == false); printf("(end main)\n"); return 0; } // begin implementation bool isOdd(int x1) { bool b1 = (x1 % 2) == 1; printf("\tisOdd(%d) is %d\n",x1,b1); return b1; } // end implementation

Here is the output of the C code.
(begin main) isOdd(2) is 0 isOdd(3) is 1 isOdd(4) is 0 (end main)

Assertions are used in debug mode.

To turn assertion checking off, in production mode, use the following at the top of the file.

To ignore assertions in a program, use the following
at the top of the program.

To go back to debug mode, comment out the above line.

Here is the code of a loop that counts and outputs values from 0.0 to 1.0, starting at 0.0 and adding 0.1 each iteration.
int i1 = 0; int n1 = 10; double x1 = 0.0; while (i1 != n1) { x1 += 0.1; i1++; printf("\ti1=%d x1=%0.20lf\n",i1,x1); }
The loop executes 10 times, so what should the value of x1 be? Here is the output of the C code.

Be very careful about making any assertions about floating point numbers when division is involved.

Here is the C code.
#include <stdio.h> #include <stdbool.h> #include <assert.h> int main() { printf("(begin main)\n"); int i1 = 0; int n1 = 10; double x1 = 0.0; while (i1 != n1) { x1 += 0.1; i1++; printf("\ti1=%d x1=%0.20lf\n",i1,x1); } /// the following assertion will fail /// assert(x1 == 1.0); printf("(end main)\n"); return 0; }

Here is the output of the C code.
(begin main) i1=1 x1=0.10000000000000000555 i1=2 x1=0.20000000000000001110 i1=3 x1=0.30000000000000004441 i1=4 x1=0.40000000000000002220 i1=5 x1=0.50000000000000000000 i1=6 x1=0.59999999999999997780 i1=7 x1=0.69999999999999995559 i1=8 x1=0.79999999999999993339 i1=9 x1=0.89999999999999991118 i1=10 x1=0.99999999999999988898 (end main)

Here is the above program with the assertion uncommented - resulting in an error.

Here is the C code.
#include <stdio.h> #include <stdbool.h> #include <assert.h> int main() { printf("(begin main)\n"); int i1 = 0; int n1 = 10; double x1 = 0.0; while (i1 != n1) { x1 += 0.1; i1++; printf("\ti1=%d x1=%0.20lf\n",i1,x1); } /// the following assertion will fail assert(x1 == 1.0); printf("(end main)\n"); return 0; }

Here is the error text of the C code.
assertion "x1 == 1.0" failed: file "D:\W\PROGRAM1.C\float31-06.c", line 17, function: main 0 [main] float31-06 1353 cygwin_exception::open_stackdumpfile: Dumping stack trace to float31-06.exe.stackdump

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