#define SIZE 50            /* Size of Stack */
#include 
int s[SIZE];
int top=-1;       /* Global declarations */

push(int elem)
{                       /* Function for PUSH operation */
    s[++top]=elem;
}

int pop()
{                      /* Function for POP operation */
    return(s[top--]);
}

main()
{                         /* Main Program */
    char pofx[50],ch;
    int i=0,op1,op2;
    printf("\n\nRead the Postfix Expression ? ");
    scanf("%s",pofx);
    while( (ch=pofx[i++]) != '\0')
    {
        if(isdigit(ch)) push(ch-'0'); /* Push the operand */
        else
        {        /* Operator,pop two  operands */
            op2=pop();
            op1=pop();
            switch(ch)
            {
            case '+':push(op1+op2);break;
            case '-':push(op1-op2);break;
            case '*':push(op1*op2);break;
            case '/':push(op1/op2);break;
            }
        }
    }
    printf("\n Given Postfix Expn: %s\n",pofx);
    printf("\n Result after Evaluation: %d\n",s[top]);
}

The post C Program for Evaluation of Postfix Expression 34*5+ first appeared on Student Projects.

#include
#include
#include
char s[20];
int top=-1;
void main()
{
    char str[20];
    char ch;
    int i;
    char pop();
    void push(char);
    int precd(char);
    s[top]='#';
    clrscr();
    printf("\n\t\tOUTPUT");
    printf("\n\tEnter the expression:");
    gets(str);
    printf("\n\tpostfix notation:");
    for(i=0;str[i]!='\0';i++)
    {
        if(isalpha(str[i]))
        {
            printf("%c",str[i]);
            continue;
        }
        if(str[i]==')')
        {
            while((ch=pop())!='(')
                printf("%c",ch);
        }
        else if(str[i]=='(')
            push(str[i]);
        else if(precd(str[i])<=precd(s[top]))
        {
            printf("%c",pop());
            push(str[i]);
        }
        else
            push(str[i]);
    }
    while(top>=0)
        printf("%c",pop());
    getch();
}
void push(char st)
{
    s[++top]=st;
}
char pop()
{
    char st;
    st=s[top--];
    return(st);
}

int precd(char s)
{
    switch(s)
    {
    case '$':return(4);
    case '*':
    case '/': return(3);
    case '+':
    case '-': return(2);
    case '(': return(1);
    case '#': return(-1);
    }
    return(0);
}

The post C program which converts given expression into its post-fix format first appeared on Student Projects.