بميـــحرلا نحنحنرلا للوللوا مــس Fundamentals of Programming C Session # 11 By: Saeed Haratian Fall 2015
Outlines Structured Programming Summary Program Modules in C Math Library Functions Function Definitions Function Prototypes
Structured Programming Summary Figure 4.17 summarizes the control statements discussed previously. Small circles are used in the figure to indicate the single entry point and the single exit point of each statement. Connecting individual flowchart symbols arbitrarily can lead to unstructured programs. Therefore, the programming profession has chosen to combine flowchart symbols to form a limited set of control statements, and to build only structured programs by properly combining control statements in two simple ways. For simplicity, only single-entry/single-exit control statements are used — there is only one way to enter and only one way to exit each control statement.
Structured Programming Summary …
Structured Programming Summary …
Structured Programming Summary … Connecting control statements in sequence to form structured programs is simple — the exit point of one control statement is connected directly to the entry point of the next, i.e., the control statements are simply placed one after another in a program — we have called this “ control-statement stacking .” The rules for forming structured programs also allow for control statements to be nested.
Structured Programming Summary … Figure 4.18 shows the rules for forming structured programs. The rules assume that the rectangle flowchart symbol may be used to indicate any action including input/output.
Structured Programming Summary … Figure 4.19 shows the simplest flowchart.
Structured Programming Summary … Applying the rules of Fig. 4.18 always results in a structured flowchart with a neat, building-block appearance. Repeatedly applying Rule 2 to the simplest flowchart (Fig. 4.19) results in a structured flowchart containing many rectangles in sequence (Fig. 4.20). Notice that Rule 2 generates a stack of control statements; so we call Rule 2 the stacking rule.
Structured Programming Summary …
Structured Programming Summary … Rule 4 generates larger, more involved, and more deeply nested structures. The flowcharts that emerge from applying the rules in Fig. 4.18 constitute the set of all possible structured flowcharts and hence the set of all possible structured programs. It’s because of the elimination of the goto statement that these building blocks never overlap one another. The beauty of the structured approach is that we use only a small number of simple single-entry/single-exit pieces, and we assemble them in only two simple ways. Figure 4.22 shows the kinds of stacked building blocks that emerge from applying Rule 2 and the kinds of nested building blocks that emerge from applying Rule 3.
Structured Programming Summary …
Structured Programming Summary … The figure also shows the kind of overlapped building blocks that cannot appear in structured flowcharts (because of the elimination of the goto statement). If the rules in Fig. 4.18 are followed, an unstructured flowchart (such as that in Fig. 4.23) cannot be created. If you’re uncertain whether a particular flowchart is structured, apply the rules of Fig. 4.18 in reverse to try to reduce the flowchart to the simplest flowchart. If you succeed, the original flowchart is structured; otherwise, it’s not. Structured programming promotes simplicity.
Structured Programming Summary …
Structured Programming Summary …
Structured Programming Summary … Bohm and Jacopini showed that only three forms of control are needed: Sequence Selection Repetition Sequence is straighforward. In fact, it’s straightforward to prove that the simple if statement is sufficient to provide any form of selection. It’s straightforward to prove that the while statement is sufficient to provide any form of repetition.
Structured Programming Summary … Combining these results illustrates that any form of control ever needed in a C program can be expressed in terms of only three forms of control: sequence if statement (selection) while statement (repetition) And these control statements can be combined in only two ways — stacking and nesting. Indeed, structured programming promotes simplicity.
Program Modules in C Most computer programs that solve real-world problems are much larger than the programs presented in the first few chapters. Experience has shown that the best way to develop and maintain a large program is to construct it from smaller pieces or modules, each of which is more manageable than the original program. This technique is called divide and conquer. This chapter describes the features of the C language that facilitate the design, implementation, operation and maintenance of large programs. The functions printf , scanf and pow that we’ve used in previous chapters are Standard Library functions.
Program Modules in C … You can write your own functions to define tasks that may be used at many points in a program. These are sometimes referred to as programmer-defined functions. The statements defining the function are written only once, and the statements are hidden from other functions. Functions are invoked by a function call, which specifies the function name and provides information (as arguments) that the called function needs to perform its designated task. A common analogy for this is the hierarchical form of management. A boss (the calling function or caller) asks a worker (the called function) to perform a task and report back when the task is done.
Program Modules in C … For example, a function needing to display information on the screen calls the worker function printf to perform that task, then printf displays the information and reports back — or returns — to the calling function when its task is completed. The boss function does not know how the worker function performs its designated tasks. The worker may call other worker functions, and the boss will be unaware of this. We’ll soon see how this “hiding” of implementation details promotes good software engineering. Note that worker1 acts as a boss function to worker4 and worker5. Relationships among functions may differ from the hierarchical structure shown in this figure.
Program Modules in C …
Math Library Functions Math library functions allow you to perform certain common mathematical calculations. Functions are normally used in a program by writing the name of the function followed by a left parenthesis followed by the argument (or a comma-separated list of arguments) of the function followed by a right parenthesis. For example, a programmer desiring to calculate and print the square root of 900.0 might write printf( "%. "%.2f" f", sqrt( , sqrt( 900.0 900.0 ) ); ) );
Math Library Functions … When this statement executes, the math library function sqrt is called to calculate the square root of the number contained in the parentheses (900.0). The number 900.0 is the argument of the sqrt function. The preceding statement would print 30.00. The sqrt function takes an argument of type double and returns a result of type double . All functions in the math library that return floating point values return the data type double . Note that double values, like float values, can be output using the %f conversion specification.
Math Library Functions …
Math Library Functions …
Functions Functions allow you to modularize a program. All variables defined in function definitions are local variables — they’re known only in the function in which they’re defined. Most functions have a list of parameters that provide the means for communicating information between functions. A function’s parameters are also local variables of that function. With good function naming and definition, programs can be created from standardized functions that accomplish specific tasks, rather than being built by using customized code. This is known as abstraction. We use abstraction each time we use standard library functions like printf , scanf and pow .
Functions There are several motivations for “functionalizing” a program. The divide-and-conquer approach makes program development more manageable. Another motivation is software reusability — using existing functions as building-blocks to create new programs. Software reusability is a major factor in the object-oriented programming movement that you’ll learn more about when you study languages derived from C, such as C++, Java and C# (pronounced “C sharp”). A third motivation is to avoid repeating code in a program. Packaging code as a function allows the code to be executed from several locations in a program simply by calling the function.
Functions …
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