Program come out with out proper execution

**mohsen** · 07-11-2013

Hello everyone the following code doesn't execute properly
( After the second entry the program comes out)!!

Code:

#include<stdio.h>
void linkfloat();
int main(){
	struct book {
					char name;
					float price;
					int page;
	};
	struct book b[3];
	int i;
	for(i=0;i<3;i++){
		printf("\nEnter name ,price and pages: ");
		scanf("%c%f%d",&b[i].name,&b[i].price,&b[i].page);//seems some thing is wrong here
	}
	printf("\n");
	for(i=0;i<3;i++){
		
		printf("%c%f%d\n",b[i].name,b[i].price,b[i].page);
	}
	
	
return 0;
}
void linkfloat(){
					float a=0,*b;
					b=&a;
					a=*b;
}

**std10093** · 07-11-2013

Is the problem relevant to the reading of a char with scanf?

Try it out.

**anduril462** · 07-11-2013

1. Fix your indentation and put some spaces around your operators and between function parameters. If your code is hard to read, it's easy to make a mistake, and hard to find or fix it.

2. Compile with warnings turned all the way up:

Code:

$ make foo
gcc -Wall -ggdb3 -std=c99 -o foo foo.c -lm -lpthread
foo.c: In function ‘main’:
foo.c:18:5: warning: format ‘%c’ expects argument of type ‘int’, but argument 2 has type ‘char *’ [-Wformat]
foo.c:18:5: warning: format ‘%f’ expects argument of type ‘double’, but argument 3 has type ‘float *’ [-Wformat]
foo.c:18:5: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘int *’ [-Wformat]

You're passing the wrong types to printf. printf and scanf behave differently, and expect different types, for each format specifier.

3. In your prototype for linkfloat on line 2, put a void inside the parentheses as well. That tells the compiler that the function takes exactly zero arguments. Without the void, the compiler doesn't know how many or what type arguments it takes, so it can't check to make sure you're calling the function correctly. I.e., the compiler would accept linkfloat(); as well as linkfloat("asdf", 123, 456.789);.

4. Generally it's a good idea to put your struct definition outside of main or any other function. If it's inside a function, only that function knows the struct type, and usually you will have more than one function that must deal with that struct type.

**mohsen** · 07-11-2013

Std10093 Thank you

**std10093** · 07-11-2013

You are welcome. It is a good thing to read anduril's post as well, since almost always he has something important to say. Moreover, we use to write

Code:

int main(void)

**anduril462** · 07-11-2013

I should have been more specific about point #2. Mismatched format specifiers for printf can result in undefined behavior, which means anything can happen. Your program may crash, it may erase your hard drive. The behavior is undefined, so anything goes. In your case, passing the wrong data to the %c, %d and %f format specifiers is most likely only going to result in garbage output. However, with format specifiers like %s, which take a pointer to the data to display, passing incorrect data may very well result in a seg fault.

**mohsen** · 07-12-2013

Thanks a lot anduril462
But one more question Do you Know any book which explains completely undefined behavior station?
I search all my c\c++ books , I couldn't find anything about that.
Thanks again

**std10093** · 07-12-2013

Well, since it is undefined behavior, we are not sure what will happen

You can have it in your mind like a severe logical error, you [U]must[U] avoid! As you gain experience, you are going to see a lot undefined behaviors coming into play

**Matticus** · 07-12-2013

You can read a version of a C standard draft, which contains a list of undefined behavior (section J2)
(Originally from this link.)

Thread: Program come out with out proper execution

Thread Tools

Search Thread

Display

Program come out with out proper execution

Similar Threads

Proper format/standard of C program?

can any one make this program run.. in proper output?

program execution

execution of a C program

Program Compiles but does not read proper file....

Tags for this Thread