Here is implementation of Macro processor in C. Here you will need to provide Assembly program containing Macro as input in MACIN.TXT. The result will be stored in MACOUT.TXT.

#include<stdio.h>
#include<conio.h>
#include<string.h>

struct mdt
{
	char lab[10];
	char opc[10];
	char oper[10];
}d[10];

void main()
{
	char label[10],opcode[10],operand[10],newlabel[10],newoperand[10];
	char macroname[10];
	int i,lines;
	FILE *f1,*f2,*f3;
	clrscr();
	f1 = fopen("MACIN.txt","r");
	f2 = fopen("MACOUT.txt","w");
	f3 = fopen("MDT.txt","w");
	fscanf(f1,"%s %s %s",label,opcode,operand);

	while(strcmp(opcode,"END")!=0)
	{
		if(strcmp(opcode,"MACRO")==0)
		{
			strcpy(macroname,label);
			fscanf(f1,"%s%s%s",label,opcode,operand);
			lines = 0;
			while(strcmp(opcode,"MEND")!=0)
			{
				fprintf(f3,"%s\t%s\t%s\n",label,opcode,operand);
				strcpy(d[lines].lab,label);
				strcpy(d[lines].opc,opcode);
				strcpy(d[lines].oper,operand);
				fscanf(f1,"%s %s %s",label,opcode,operand);
				lines++;
			}
		}
		else if(strcmp(opcode,macroname)==0)
		{
			printf("lines=%d\n",lines);
			for(i=0;i<lines;i++)
			{
				fprintf(f2,"%s\t%s\t%s\n",d[i].lab,d[i].opc,d[i].oper);
				printf("DLAB=%s\nDOPC=%\nDOPER=%s\n",d[i].lab,d[i].opc,d[i].oper);
			}
		}
		else
		fprintf(f2,"%s\t%s\t%s\n",label,opcode,operand);
		fscanf(f1,"%s%s%s",label,opcode,operand);
	}
	fprintf(f2,"%s\t%s\t%s\n",label,opcode,operand);
	fclose(f1);
	fclose(f2);
	fclose(f3);
	printf("FINISHED");
	getch();
}

Assembly program as input (MACIN.TXT)

CALC START 1000
SUM MACRO **
** LDA #5
** ADD #10
** sTA 2000
** MEND **
** LDA LENGTH
** COMP ZERO
** JEQ LOOP
** SUM **
LENGTH WORD S
ZERO WORD S
LOOP SUM **
** END **

Macro definition table (MDT.TXT)

**	LDA	#5
**	ADD	#10
**	sTA	2000

Output (MACOUT.TXT)

CALC	START	1000
**	LDA	LENGTH
**	COMP	ZERO
**	JEQ	LOOP
**	LDA	#5
**	ADD	#10
**	sTA	2000
LENGTH	WORD	S
ZERO	WORD	S
**	LDA	#5
**	ADD	#10
**	sTA	2000
**	END	**