# include <stdio.h>
# include <string.h>
# define MAX 20
void infixtoprefix(char infix[20],char prefix[20]);
void reverse(char array[30]);
char pop();
void push(char symbol);
int isOperator(char symbol);
int prcd(symbol);
int top=-1;
char stack[MAX];
main() {
	char infix[20],prefix[20],temp;
	printf("Enter infix operation: ");
	gets(infix);
	infixtoprefix(infix,prefix);
	reverse(prefix);
	puts((prefix));
}
//--------------------------------------------------------
void infixtoprefix(char infix[20],char prefix[20]) {
	int i,j=0;
	char symbol;
	stack[++top]='#';
	reverse(infix);
	for (i=0;i<strlen(infix);i++) {
		symbol=infix[i];
		if (isOperator(symbol)==0) {
			prefix[j]=symbol;
			j++;
		} else {
			if (symbol==')') {
				push(symbol);
			} else if(symbol == '(') {
				while (stack[top]!=')') {
					prefix[j]=pop();
					j++;
				}
				pop();
			} else {
				if (prcd(stack[top])<=prcd(symbol)) {
					push(symbol);
				} else {
					while(prcd(stack[top])>=prcd(symbol)) {
						prefix[j]=pop();
						j++;
					}
					push(symbol);
				}
				//end for else
			}
		}
		//end for else
	}
	//end for for
	while (stack[top]!='#') {
		prefix[j]=pop();
		j++;
	}
	prefix[j]='\0';
}
////--------------------------------------------------------
void reverse(char array[30]) // for reverse of the given expression {
	int i,j;
	char temp[100];
	for (i=strlen(array)-1,j=0;i+1!=0;--i,++j) {
		temp[j]=array[i];
	}
	temp[j]='\0';
	strcpy(array,temp);
	return array;
}
//--------------------------------
char pop() {
	char a;
	a=stack[top];
	top--;
	return a;
}
//----------------------------------
void push(char symbol) {
	top++;
	stack[top]=symbol;
}
//------------------------------------------
int prcd(symbol) // returns the value that helps in the precedence {
	switch(symbol) {
		case '+':
		        case '-':
		        return 2;
		break;
		case '*':
		        case '/':
		        return 4;
		break;
		case '$':
		        case '^':
		        return 6;
		break;
		case '#':
		        case '(':
		        case ')':
		        return 1;
		break;
	}
}
//-------------------------------------------------
int isOperator(char symbol) {
	switch(symbol) {
		case '+':
		        case '-':
		        case '*':
		        case '/':
		        case '^':
		        case '$':
		        case '&':
		        case '(':
		        case ')':
		        return 1;
		break;
		default:
		        return 0;
		// returns 0 if the symbol is other than given above
	}
}
by

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Read inputs from stdin

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#include <stdio.h>
int main()
{
    char name[50];
    printf("Enter name:");
    scanf("%s", name);
    printf("Hello %s \n" , name );
    return 0;
    
}

About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}