C Programming - Library Functions - Discussion

ungetc() pushes a character back into input stream.

That is it enable us to reenter the char as it pushes b into input stream again and again if you comment ungetc(c,stdin) you will able to enter input 5 times.
Also a second call to ungetc without getc will force the previous character to be forgotten so here
When you use ungetc(c, stdout) first it will get printed and pushes the cha back so printf also not print it and for next time we call it without calling getc so it makes it to forgotten the prev char hence it is only one time prints.

If you comment ungetc(c, stdout) you will get b 5 times.
And if you comment both ungetc it will take one char and print it.

Please explain the use of ungetc().

ungetc(c, stdout);

Statement is invalid statement.
Program will be crashed by this message:
Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

And the output will be : bbbbb.
If we remove ungetc(c, stdout); statement.

I run the program then give output is-ppppp.

But how it will possible, where the answer is b.

Please. Can someone elaborate how the output is b?

What is the use of ungetc function in this code as the output is bbbbb which is same as printf?

Any explanation please?

I got the output as -> bbbbb which is option (B) and not option (C).

#include<stdio.h>

int main()
{
int i;
char c;
for(i=1; i<=5; i++)
{
scanf("%c", &c); /* given input is 'b' */
ungetc(c, stdout);


}
return 0;
}

If I run this code i got answer b. Means ungetc function work as printf.

But my problem is if ungetc send their input to monitor then it should be printed and then next b should be printed because of printf.

Although the answer is correct but i am not able to get the logic.

I don't get above logic. Even whenever I'm running this program that time an error msg comes that is core dumped.

scanf function reads the char c from i/p stream stdin (which is the input b), ungetc(c,stdout)(get unsigned char) pushes c to stdout(the monitor), printf also pushes the char c to output screen.

ungetc(c,stdin) pushes back the char to input stream stdin...this c is read again when scanf is implemented in next loop.

Notice that ungetc can b used only for 1 byte of data...hence first use of ungetc is forgotten and the o/p is only b (as a result of printf...).