Conversions in C

[dianagaby2002]

I don't understand these conversions in C I have for homework. Could you explain me or give some links?

1)Given int n= 200, m= 200;
long r;
And supposing sizeof(int) is 2, what is the result of: r = n*m; ?

Answer is -25536

Why?

2)Given static int i, t[10]; i and t are not explicit initialised

Which will be the result of the expression:
(i=0) || (t[i] <0)

Result is 1

3) a) Given char c = 130;

c will become -126

b) What will the following sequence return for this input: 20?

#include<stdio.h>
void main(){
char a;
scanf("%c", &a);
printf("%c", a);
}

Result is: 2

Thank you!

[donbock]

Please refer to posting coursework questions and answers.

I'll give you some hints...

Question 1 not only assumes sizeof(int) is 2, but it also assumes that negative numbers are represented in two's-complement format (this is nearly always the case).

Question 2 says the variables "are not explicitly initialized". What are the non-explicit ways for variables to be initialized? By the way, the expression should be:
(i==0) || (t[i] <0)

Question 3a assumes that type char is signed (it needn't be) and that negative numbers are represented in two's-complement format.

Question 3b; I suppose you mean that the input is the two characters '2' and '0'. Review the manpages for scanf and printf to see precisely how each interprets the %c format specifier. This question probably assumes that stdin and stdout are unbuffered.

You should look up the following terms if you are not familiar with them:

• two's-complement
• buffered I/O
• nonbuffered I/O or unbuffered I/O

[weaknessforcats]

Question 1 assumes sizeof(long) is 2. long is guaranteed to be the sizeof an int but may be longer. So is the answer here is indeterminate.

Question 2 is 1. static int is initialized to 0 by default.

Question 3a is bad code. 130 is larger than a char, unless the char is unsigned. Your compiler should give a warning here.

Question 3b, scanf only reads one byte into a char. You get the 2 of 20.

[donbock]

Regarding the assumptions for question 1...

The C Standard guarantees that sizeof(int) is no smaller than 2; but it might be larger. The Standard goes on to guarantee that sizeof(long) is no smaller than 4 or sizeof(int), whichever is bigger; but it might be larger.

I believe that the Question 1 answer reported by the OP is fully explained by:
> the assumption that sizeof(int) is 2;
> the assumption that negative numbers are represented by two's complement format; and
> the fact [not assumption] that sizeof(long) > 2.

Another hint for Q1... the following code snippet has a different value for r than reported by the OP for Q1.

int n = 200;
long m = 200;
long r;
r = n * m;
printf("%ld\n",r);