Merge pull request matthewsamuel95#686 from pockemon/patch1

Added infix to postfix and prefix conversion using stack

Author: matthewsamuel95

Data Structures/Stack/Infix to postfix conversion using stack.c

@@ -0,0 +1,108 @@
+#include<stdio.h>
+#include<string.h>
+#define size 100
+int top=-1;
+char stack[size];
+int is_operator(char symbol);
+char pop();
+void push(char item);
+int precendence(char symbol);
+
+int main()
+{
+  char infix[size],postfix[size],item;
+  char temp;
+  int i=0,j=0;
+  printf("enter infix expression\n");
+  scanf("%s",infix);
+  while(infix[i]!='\0')
+   {
+    item=infix[i];
+    if(item=='(')
+    {
+       push(item);
+    }
+    else if(item>='a'&& item<='z'||item>='A'&& item<='Z')
+    {
+      postfix[j]=item;
+      j++;
+     }
+    else if(is_operator(item)==1)
+    {
+      temp=pop();
+      while(is_operator(temp)==1 && precendence(temp)>=precendence(item))
+      {
+       postfix[j]=temp;
+       j++;
+       temp=pop();
+      }
+     push(temp);
+     push(item);
+    }
+    else if(item==')')
+    {
+      temp=pop();
+      while(temp!='(')
+     {
+      postfix[j]=temp;
+      j++;
+      temp=pop();
+     }
+   }
+   else
+   {
+       printf("\n invalid\n");
+       exit(0);
+   }
+   i++;
+  }
+  while(top>-1)   //for no paranthesis
+  {
+    postfix[j]=pop();
+    j++;
+  }
+  postfix[j]='\0';
+  printf("the postfix expression is\n");
+  printf("%s",postfix);
+  return 0;
+}
+
+void push(char item)
+{
+    if(top>=size-1)
+    printf("stack overfloaw\n");
+    else
+    {
+     top++;
+     stack[top]=item;
+    }
+}
+ 
+int is_operator(char symbol)
+{
+    if(symbol=='^'||symbol=='+'||symbol=='-'||symbol=='*'||symbol=='/')
+        return 1;
+    else
+        return 0;
+
+}
+
+char pop()
+{
+    char item;
+    item=stack[top];
+    top--;
+    return item;
+}
+
+int precendence(char symbol)
+{
+    if(symbol=='^')
+       return 3;
+    else if(symbol=='/'||symbol=='*')
+       return 2;
+    else if(symbol=='+'||symbol=='-')
+        return 1;
+    else
+        return 0;
+}

Data Structures/Stack/Infix to prefix conversion using stack.c

@@ -0,0 +1,101 @@
+#include<stdio.h>
+#include<string.h>
+#define size 100
+int top=-1;
+char stack[size];
+int is_operator(char symbol);
+char pop();
+void push(char item);
+int precendence(char symbol);
+int main()
+{
+  char infix[size],prefix[size],item;
+  char temp;
+  int i=0,j=0,len;
+  printf("enter infix expression\n");
+  gets(infix);
+  len=strlen(infix);
+  for(i=len;i>=0;i--)
+  {
+   item=infix[i];
+   if(item==')')
+   {
+    push(item);
+   }
+   else if(item>='a'&& item<='z'||item>='A'&& item<='Z')
+   {
+    prefix[j]=item;
+    j++;
+   }
+   else if(is_operator(item)==1)
+   {
+    temp=pop();
+    while(is_operator(temp)==1 && precendence(temp)>=precendence(item))
+    {
+     prefix[j]=temp;
+     j++;
+     temp=pop();
+    }
+    push(temp);
+    push(item);
+   }
+   else if(item=='(')
+   {
+     temp=pop();
+     while(temp!=')')
+     {
+      prefix[j]=temp;
+      j++;
+      temp=pop();
+     }
+   }
+  }
+  while(top>-1)
+  {
+    prefix[j]=pop();
+    j++;
+  }
+  prefix[j]='\0';
+  printf("the prefix expression is\n");
+  printf("%s",strrev(prefix));
+  return 0;
+}
+
+void push(char item)
+ {
+    if(top>=size-1)
+    printf("stack overfloaw\n");
+    else
+    {
+     top++;
+     stack[top]=item;
+    }
+}
+
+int is_operator(char symbol)
+{
+    if(symbol=='^'||symbol=='+'||symbol=='-'||symbol=='*'||symbol=='/')
+        return 1;
+    else
+        return 0;
+}
+ 
+char pop()
+{
+    char item;
+    item=stack[top];
+    top--;
+    return item;
+}
+  
+int precendence(char symbol)
+{
+    if(symbol=='^')
+       return 3;
+    else if(symbol=='/'||symbol=='*')
+       return 2;
+    else if(symbol=='+'||symbol=='-')
+        return 1;
+    else
+        return 0;
+ }