Understanding the "C" program

Understanding the program

In the program you saw above, the information enclosed between ‘/* */’ is called a ‘comment’ and may appear anywhere in a C program. Comments are optional and are used to increase the readability of the program.

The ‘#include’ in the first line of the program is called a preprocessor directive. A preprocessor is a program that processes the C program before the compiler. All the lines in the C program beginning with a hash (#) sign are processed by the preprocessor.

‘stdio.h’ refers to a file supplied along with the C compiler. It contains ordinary C statements. These statements give information about many other functions that perform input-output roles.

Thus, the statement ‘#include’ effectively inserts the file ‘stdio.h’ into the file hello.c making functions contained in the ‘stdio.h’ file available to the programmer. For example, one of the statements in the file ‘stdio.h’ provides the information that a function printf() exists, and can accept a string (a set of characters enclosed within the double quotes).

The next statement is the main() function. As you already know, this is the place where the execution of the C program begins. Without this function, your C program cannot execute.

Next comes the opening brace ‘{’, which indicates the beginning of the function. The closing brace ‘}’ indicates the end of the function.

The statement printf() enclosed within the braces‘{}’ informs the compiler to print (on the screen) the message enclosed between the pair of double quotes. In this case, ‘Hello, world’ is printed. As mentioned earlier, the statement printf() is a built-in function shipped along with the C compiler. Many other built-in functions are available that perform specific tasks. The power of C lies in these functions.

Be cautious about errors!

Errors/bugs are very common while developing a program. If you don't detect them and correct them, they cause a program to produce wrong results. There are three types of errors — syntax, logical, and run-time errors. Let us look at them:

1. Syntax errors: These errors occur because of wrongly typed statements, which are not according to the syntax or grammatical rules of the language. For example, in C, if you don’t place a semi-colon after the statement (as shown below), it results in a syntax error.

printf(“Hello,world”) – error in syntax (semicolon missing)

printf("Hello,world"); - This statement is syntactically correct.

2. Logical errors: These errors occur because of logically incorrect instructions in the program. Let us assume that in a 1000 line program, if there should be an instruction, which multiplies two numbers and is wrongly written to perform addition. This logically incorrect instruction may produce wrong results. Detecting such errors are difficult.

3. Runtime errors: These errors occur during the execution of the programs though the program is free from syntax and logical errors. Some of the most common reasons for these errors are

1. when you instruct your computer to divide a number by zero.
2. when you instruct your computer to find logarithm of a negative number.
3. when you instruct your computer to find the square root of a negative integer.

Unless you run the program, there is no chance of detecting such errors.

Try it out

1. Write a C program to print your name on the screen.

2. Write a C program to print the name of your favorite cricketer.