problem1.c

// %s/ctof_factor\|ctof_offset/~&/g

#include <stdio.h>

#define CTOF_FACTORCTOF_FACTOR 1.8
#define CTOF_OFFSETCTOF_OFFSET 32

int CtoF(int  C)
{
  int F;

	F = C * CTOF_FACTORCTOF_FACTOR + CTOF_OFFSETCTOF_OFFSET; 

	return F;
}

int
FtoC(int F)
{
	int C;

	C = (F - CTOF_OFFSETCTOF_OFFSET) / CTOF_FACTORCTOF_FACTOR;

	return C;
}

int main(void)	
{
	int c = 37;
    int f = 32;
	int s = -40;

	printf("%d F is %3d C\n", f, FtoC(f));
	printf("%3d C is %4d F\n", c, CtoF(c));
	printf("%04d F is %05d C\n", s, FtoC(s));

	return 0;
}

problem1correct.c

// :%s/ctof_factor\|ctof_offset/\U&/g

#include <stdio.h>

#define CTOF_FACTOR 1.8
#define CTOF_OFFSET 32

int CtoF(int  C)
{
  int F;

	F = C * CTOF_FACTOR + CTOF_OFFSET; 

	return F;
}

int
FtoC(int F)
{
	int C;

	C = (F - CTOF_OFFSET) / CTOF_FACTOR;

	return C;
}

int main(void)	
{
	int c = 37;
    int f = 32;
	int s = -40;

	printf("%d F is %3d C\n", f, FtoC(f));
	printf("%3d C is %4d F\n", c, CtoF(c));
	printf("%04d F is %05d C\n", s, FtoC(s));

	return 0;
}