Requirement: Input a program, analyze the identifiers, basic words, operators, delimiters, constants and output
Algorithm idea: first define a two-dimensional array, store the read program segment, and then process the two-dimensional array
The specific processing method is: first read a character, if it is a letter or number, continue to read it later, if it is of the same type, store it in a temporary array (if it is a letter, compare it with the reserved word to determine whether it is a reserved word, If it is a number, output it), otherwise jump out and make a judgment; if it is an operator, judge the current character and the next character, and judge whether it is two consecutive operators such as >= or <=; the delimiter is judged directly.
Above code:
#include<stdio.h>
#include<string.h>
#include <stdbool.h> //Introduce boolean type, there is no boolean type in stdio.h file
#define lineLength 100 //fix the length of each line
#define primLength 10 //The length of the read string (identifier, etc.)
#define numLength 20 //The length of the read constant
//Store the basic word
char mPrimary[13][20]= {"begin","call", "const","do","end","if","odd","procedure","read","then","var","while","write"};//Order, The premise of binary search is order (in alphabetical order)
char text[lineLength][lineLength];//Store the read content
void main()
{
int i=0;
bool flag=false; //Determine whether the input is over , and whether the last marker (.) of the two-dimensional array is read, and the pl/0 language program ends with a dot.
//read input into a 2D character array
int t;
for (t = 0; t < 100;
if (!*text[t]) //When the input row is empty if the condition is satisfied, execute the break statement to jump out of the loop.
{
break;
}
}
//Process the two-dimensional character array,
int mid;
for(i=0; i<t; i++)
{
char prim[primLength];//Create a new character array to store basic words or variables Name
char num[numLength];//Create a new character array to store constants
for(mid=0; mid<primLength; mid++) //Empty the array
prim[mid]='\0';
for(mid=0; mid <numLength; mid++) //clear the array
num[mid]='\0';
int j;
for(j=0; text[i][j]!='\0'; j++)
{
if(text[i ][j]=='.')
{
printf(". delimiter/terminator\n");
flag=true;
break;
}
else if(text[i][j]==' ')
{
continue;
}
else if(text[i][j]>='a'&&text[i][j]<= 'z')
{
for(mid=0; (text[i][j]>='a'&&text[i][j]<='z')||(text[i][j]>=' 0'&&text[i][j]<='9'); j++,mid++) //Read in the string
prim[mid]=text[i][j];
j--;//Because j is used to judge At the end of the loop, one character needs to be returned here
for(mid=0; prim[mid]!='\0'; mid++) //output string
printf("%c",prim[mid]);
int head =0,tail=12;//Binary search,Find whether it is a basic word, there are 13 reserved words
int mid2;//Intermediate comparison variable
while(head<=tail)
{
mid2=(head+tail)/2;
if(strcmp(prim,mPrimary[mid2])<=0) //String comparison uses strcpy() function
tail=mid2-1;
if (strcmp(prim,mPrimary[mid2])>=0)
head=mid2+1;
}
if(head-1>tail)//The search is successful, it is determined as the basic word
printf("Basic word/%s \n", mPrimary[mid2]);
else
printf("identifier\n");
for(mid=0; prim[mid]!='\0'; mid++) //Empty the array for next time read
prim[mid]= '\0';
}
else if(text[i][j]>='0'&&text[i][j]<='9')
{
for(mid=0; text[i][j]>='0'&&text[i][j]<='9'; j++,mid++)//Read in numbers
num[mid]=text[i] [j];
j--;//Because j is used to judge the end of the loop, a character needs to be returned here
for(mid=0; num[mid]!='\0'; mid++) //Output numbers, And clear it for next time reading
{
printf("%c",num[mid]);
num[mid]='\0';
}
printf(" constant\n");
}
else//processing "+ - * /,#() etc"
{
switch(text[i][j])
{
case '<':
{
if(text[i][j+1]=='=')
{
printf("%c%c operator/less than or equal sign\n",text[i][j],text[i][j+1]);
j++;
}
else
{
printf("%c operator\n ",text[i][j]);
}
break;
}
case '>':
{
if(text[i][j+1]=='=')
{
printf("%c%c operator/greater than Equal sign\n",text[i][j],text[i][j+1]);
j++;
}
else
{
printf("%c operator\n",text[i][j]);
}
break;
}
case ':':
{
if(text[i][j+1]=='=')
{
printf( "%c%c operator\n",text[i][j],text[i][j+1]);
j++;
}
else
{
printf("%c operator\n",text[i] [j]);
}
break;
}
case '+':
case '-':
case '*':
case '/':
{
printf("%c operator\n",text[i][j]);
break;
}
case '(':
{
printf("%c delimiter\n",text[i] [j]);
break;
}
case ')':
{
printf("%c delimiter\n",text[i][j]);
break;
}
case ',':
{
printf("%c delimiter /comma\n",text[i][j]);
break;
}
case ';':
{
printf("%c delimiter/semicolon\n",text[i][j]);
break;
}
default:
printf("%c identifier\n",text[i][j]);
}
}
}
if(flag)
break;
}
}
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