Exercise 1-9 from The C Programming Language by Brian W. Kernighan, Dennis M. Ritchie​ "Write a program to copy its input to its output replacing each string of one or more blanks by a single blank"

TheCProgrammingLanguage_Exercise1_9.c

#include <stdio.h>

main(){
	int c;
	while((c = getchar()) != EOF){
		putchar(c);
		if(c == ' '){
			while((c = getchar()) == ' ')
				;
			putchar(c);
		}
	}
	//Use ctrl+D on unix systems to output an EOF to stdin
}

//symmetrical formatting

If you compile this with:
$ cc TheCProgrammingLanguage_Exercise1_9.c

Then run:
$ ./a.out < TheCProgrammingLanguage_Exercise1_9.c

You'll end up with the file outputted with extra spaces removed. Useful for a formatting tool.

that's an elegant solution!