THREE ADDRESS CODE GENERATION [ System Software Lab ]

Ex. No.: 12

THREE ADDRESS CODE GENERATION

AIM :

            To write a C program to generate a three address code for a given expression.

ALGORITHM:

Step1: Begin the program

Step2 : The expression is read from the file using a file pointer

Step3 : Each string is read and the total no. of strings in the file is calculated.

Step4: Each string is compared with an operator; if any operator is seen then the previous string and next string are concatenated and stored in a first temporary value and the three address code expression is printed

Step5 : Suppose if another operand is seen then the first temporary value is concatenated to the next string using the operator and the expression is printed.

Step6 : The final temporary value is replaced to the left operand value.

Step7 : End the program.

PROGRAM:  //program for three address code generation

#include<stdio.h>

#include<conio.h>

#include<stdlib.h>

#include<string.h>

struct three

{

char data[10],temp[7];

}s[30];

void main()

{

char d1[7],d2[7]="t";

int i=0,j=1,len=0;

FILE *f1,*f2;

clrscr();

f1=fopen("sum.txt","r");

f2=fopen("out.txt","w");

while(fscanf(f1,"%s",s[len].data)!=EOF)

len++;

itoa(j,d1,7);

strcat(d2,d1);

strcpy(s[j].temp,d2);

strcpy(d1,"");

strcpy(d2,"t");

if(!strcmp(s[3].data,"+"))

{

fprintf(f2,"%s=%s+%s",s[j].temp,s[i+2].data,s[i+4].data);

j++;

}

else if(!strcmp(s[3].data,"-"))

{

fprintf(f2,"%s=%s-%s",s[j].temp,s[i+2].data,s[i+4].data);

j++;

}

for(i=4;i<len-2;i+=2)

{

itoa(j,d1,7);

strcat(d2,d1);

strcpy(s[j].temp,d2);

if(!strcmp(s[i+1].data,"+"))

fprintf(f2,"\n%s=%s+%s",s[j].temp,s[j-1].temp,s[i+2].data);

else if(!strcmp(s[i+1].data,"-"))

fprintf(f2,"\n%s=%s-%s",s[j].temp,s[j-1].temp,s[i+2].data);

strcpy(d1,"");

strcpy(d2,"t");

j++;

}

fprintf(f2,"\n%s=%s",s[0].data,s[j-1].temp);

fclose(f1);

fclose(f2);

getch();

}

Input:  sum.txt

out = in1 + in2 + in3 - in4

Output  :       out.txt

t1=in1+in2

t2=t1+in3

t3=t2-in4

out=t3

RESULT:

            Thus a C program to generate a three address code for a given expression is written, executed and the output is verified.

Ex. No.: 13

GENERATION OF ASSEMBLY LANGUAGE INSTRUCTION FROM THREE ADDRESS CODE

AIM :

            To write a C program to generate an assembly language instruction from three address code.

ALGORITHM:

Step1 : Begin the program

Step2 : The file containing the three address code is given as input to this program

Step3 : Each string is read from the file

Step4 : In an expression the string the left of the operator is printed with the ‘LDA’ string.

Step5 : Next if the operator is ‘+’ then ‘ADO’ is printed else ‘SUB’ is printed followed  by the string to the right of the operator.

Step6 : Then ‘STA’ string is printed followed by the string value left of the ‘=’ operator

Step7 : .End of the program

PROGRAM: //GENERATION OF ASSEMBLY LANGUAGE INSTRUCTION FROM THREE ADDRESS CODE

#include<stdio.h>

#include<conio.h>

#include<string.h>

struct three

{

char data[10],temp[7];

}s[30];

void main()

{

            char *d1,*d2;

            int i=0,len=0;

            FILE *f1,*f2;

            clrscr();

            f1=fopen("exe1.txt","r");

            f2=fopen("exe2.txt","w");

            while(fscanf(f1,"%s",s[len].data)!=EOF)

            len++;

            for(i=0;i<=len;i++)

            {

             if(!strcmp(s[i].data,"="))

             {

             fprintf(f2,"\nLDA\t%s",s[i+1].data);

             if(!strcmp(s[i+2].data,"+"))

             fprintf(f2,"\nADD\t%s",s[i+3].data);

             if(!strcmp(s[i+2].data,"-"))

             fprintf(f2,"\nSUB\t%s",s[i+3].data);

             fprintf(f2,"\nSTA\t%s",s[i-1].data);

             }

     }

     fclose(f1);

     fclose(f2);

     getch();

 }

Input: exe1.txt

t1 = in1 + in2

t2 = t1 + in3

t3 = t2 - in4

out = t3

Output: exe2.txt

LDA    in1

ADD   in2

STA    t1

LDA    t1

ADD   in3

STA    t2

LDA    t2

SUB    in4

STA    t3

LDA    t3

STA    out

RESULT:

            Thus a   C program to generate a assembly language instruction from three address code is written, executed and the output is verified.