postfix evaluation new

#include<stdio.h>

void sum();
void diff();
void mult();
void div();
void power();
int s[100],top=-1;
void main(){
    char st[30];
    int i;
    printf("enter postfix");
    scanf("%[^\n]s",st);
    for(i=0;st[i]!='\0';i++){
        if(st[i]!=' '){
            switch(st[i]){
                case '+':
                sum();
                break;
                case '-':
                diff();
                break;
                case '*':
                mult();
                break;
                case '/':
                div();
                break;
                case '^':
                power();
                break;
                default:
                top++;
                s[top]=st[i]-48;
            }
        }
    }
    printf("result is %d",s[top]);
}
void sum(){
    int res,op1,op2;
    op1=s[top];
    top--;
    op2=s[top];
    top--;
    res=op2+op1;
    top++;
    s[top]=res;
}
void diff(){
    int res,op1,op2;
    op1=s[top];
    top--;
    op2=s[top];
    top--;
    res=op2-op1;
    top++;
    s[top]=res;
}
void mult(){
int res,op1,op2;
    op1=s[top];
    top--;
    op2=s[top];
    top--;
    res=op2*op1;
    top++;
    s[top]=res;
            }
            void div(){
                int res,op1,op2;
    op1=s[top];
    top--;
    op2=s[top];
    top--;
    res=op2/op1;
    top++;
    s[top]=res;
            }
            void power(){
            int res,op1,op2,i;
    op1=s[top];
    top--;
    op2=s[top];
    top--;
    for(i=0;i<op1;i++){
        res=res*op2;
    }
    
            }