Operator precedence parsing algorithm

//This is operator precedence parsing algorithm using C

char pre[10][10],ss[30],rs[30],stk[10][2];

int i,j,k,n,p,sp=0,br=0;

void push();

void pop();

char chk_pre();

void reduce_ss();

void main()

{

clrscr();

strcpy(pre[0]," +*()]");

strcpy(pre[1],"+><<>>");

strcpy(pre[2],"*>><>>");

strcpy(pre[3],"(<<<=e");

strcpy(pre[4],")>>e>>");

strcpy(pre[5],"[<<<e=");

n=6;

scanf ("%s",ss, printf("Enter the source string : "));

strcpy(rs,"[");

strcat(rs,ss);

strcat(rs,"]");

strcpy(ss,rs);

printf("\n");

for(i=0;i<n;i++)

{

for(j=0;j<strlen(pre[i]);j++)

printf("%c\t",pre[i][j]);

printf("\n");}

while(ss[2]!=']' && br==0)

{

sp=0;

for(i=0;i<strlen(ss);i++)

{

if( (ss[i]>='a' && ss[i]<='z') || (ss[i]>='A' && ss[i]<='Z') )

continue;

push();

if(stk[sp-1][1]=='e' || ss[1]==']' || ss[0]==']')

{ printf("\n\nInvalid string.");

br=1;

break; }

if((stk[sp-1][1]=='>' && stk[sp-2][1]=='<') || stk[sp-1][1]=='=')

{ reduce_ss();

pop(); } } }

if(ss[2]==']')

printf("\nValid String.");

getch();

}

void push()

{ stk[sp][0]=ss[i];

stk[sp][1]=chk_pre();

sp++; }

void pop()

{ char tmp,tmp1;

sp--;

tmp=stk[sp][0];

tmp1=stk[sp][1];

sp--;

stk[sp][0]=tmp;

stk[sp][1]=tmp1;

sp++; }

char chk_pre()

{ char tmp;

if(i==0)

tmp=' ';

else

{ for(j=0;j<n;j++)

for(k=0;k<strlen(pre[j]);k++)

if(stk[sp-1][0]==pre[j][0] && stk[sp][0]==pre[0][k])

tmp=(pre[j][k]); }

return tmp; }

void reduce_ss()

{  char t1[30],t3[30];

int tmp;

if(stk[sp-1][0]==')' && stk[sp-2][0]=='(')

tmp=i-2;

else

tmp=i-3;

for(j=0;j<tmp;j++)

{  t1[j]=ss[j];  }

t1[j]='\0';

tmp=tmp+3;

k=0;

for(j=tmp;j<strlen(ss);j++)

{  t3[k]=ss[j];

k++;  }

t3[k]='\0';

strcpy(ss,"");

strcpy(ss,t1);

strcat(ss,"i");

strcat(ss,t3);

}