Dare To Debug

Taken from: Let Us C, page 638 -644

C programmers are great inventors of our times. However, there are is no shortage of horror stories about programs that took twenty times to DEBUG as they did to WRITE. Many a time programs had to be rewritten all over again because the bugs present in them could not be located. Bugs are C programmer’s birththright. But how do we chase them away. No sure-shot way for that. I thought if I make a list of more common programming mistakes, it might be a help. They are not arranged in any particular order. But as you realize, surely a great help!

[1] Omitting ampersand(&) before the variables using in scanf(). For example:

	int choice;

	scanf("%d",choice);

Here, the & i.e ampersand is missing.

Another common mistakes with scanf() is to give blanks either just before the format string or immediately after the format string as in;

	int choice;

	scanf(" %d ",%choice);

Note that it is not a mistake but till you are not going to understand scanf() it will trouble you. Safety is in avoiding the blanks.

[2] Using the operator = instead of the operator ==. Note that = is used for assignmet while == is used for equality. In C equal to is not equal to equal to. for eg; int i=10;

	while(i=10)

	{
		printf("got to get out");
		i++;

	}

Here the while loop become an infinite loop since every time, instead of checking the value of i against 10, it assigns the value 10 to i. As 10 is a non zero value the will be always true.

[3] Ending a loop with a semicolon.Observes the following program;

int j=1;
while(j<=10);
j++;

Here, inadverently, we have fallen in an indefinite loop. Cause is the semicolon after the while loop. the semicolon is treated as the null statement by the compiler as shown below

while(j<=10)
	;

This is an indefinite loop,since the null statement keeps getting executed indefinitely as j never gets the increament.

[4] Using continue in a switch. It is a common error to believe that the way the keyword break is used with loops and a switch; similarly the keyword continue can also be used with them. Remember that continue works only with loops, never with switch.

[5] Forgetting the bound of an array. Note in C we don’t have bound checking so it is upto you how you deal with this.

int num[50], i;

for(i = 0; i <= 50; ++i)

	num[i] = i * i;

Here, in the array num, there is no such element as num[50], since array counting begins with 0 and not 1. Compiler would not give a warining if our program exceeds the bounds. If no taken care of, in extremes cases, the above code might even hang the computer.

Always Remember

Programming is not about being clever and obscure -- it's about how clearly your program communictate it's purpose.

Code conciseness is much more less important than code readability.

Reduction in program size necessarily doesn't mean reduction in meaning for the next programmers.

Any person can write the program which computer can understad, but real programmer write program which human can understand.

Debugging in C

Keep It Simple Sir

Dare To Debug

Always Remember