Beginner’s Guide to Writing Your First C Language Program

#include
#include
int main(int argc, char *argv[]) {
double num1, num2, result; // Declare variables
char op;
printf(“Please enter the first number:”);
scanf(“%lf”, &num1);
printf(“Please enter the operator:”);
scanf(” %c”, &op);
printf(“Please enter the second number:”);
scanf(“%lf”, &num2);
switch(op) { // Perform corresponding calculations based on the operator
case ‘+’:
result = num1 + num2;
break;
case ‘-‘:
result = num1 – num2;
break;
case ‘*’:
result = num1 * num2;
break;
case ‘/’:
if(num2 == 0) { // Handle division by zero
printf(“Error: Division by zero\n”);
exit(1);
}
result = num1 / num2;
break;
default: // Handle invalid operators
printf(“Error: %c is an invalid operator\n”, op);
exit(1);
}
printf(“%.2f %c %.2f = %.2f\n”, num1, op, num2, result);
return 0;
}

#define STACK_SIZE 128 double eval_expr(char* expr) { // Define operator stack and operand stack char op_stack[STACK_SIZE]; double num_stack[STACK_SIZE]; For each token in expr: If token is an operand: Parse token as operand and push onto num_stack If token is an operator: While op_stack is not empty and the top operator’s precedence >= token’s precedence: Pop the top operator from op_stack, pop two operands from num_stack to perform the operation, and push the result onto num_stack Push token onto op_stack While op_stack is not empty: Pop the top operator from op_stack, pop two operands from num_stack to perform the operation, and push the result onto num_stack return the top element of num_stack; }

// After pushing “3 * 4” onto the stack, the data in the stack is as follows num_stack = [3, 4]; op_stack = [*]; // When encountering the + sign, its precedence is lower than *, pause pushing, calculate 3 * 4 first, then push the result 12 onto the stack num_stack = [12]; op_stack = [+]; // After pushing “(2-1” onto the stack, the data is as follows num_stack = [12, 2, 1]; op_stack = [+, (, -]; // When encountering the right parenthesis, stop pushing, match the left parenthesis, and pop data from the stack to calculate num_stack = [12, 1]; op_stack = [+]; // After pushing “/5^2” onto the stack, the data is as follows num_stack = [12, 1, 5, 2]; op_stack = [+, /, ^]; // Next, pop the data to calculate, obtaining the result num_stack = [12.04]; op_stack=[];