teaching machines

CS 330 Lecture 13 – Strings and structs

February 20, 2012 by Chris Johnson. Filed under cs330, lectures, spring 2012.

Agenda

• array out-of-bounds
• strings null-terminated char arrays
• strlen
• strcat
• strcpy
• strdup
• strcmp
• structs
• header files
• a stack API
• evaluating postfix expressions
• for each token
• if token is number, push it on operand stack
• if token is operator, pop two operands, push result back on
• pop stack to get the value

Code

makefile

EXES = first arrays months oob strings

all: $(EXES)

$(EXES): %: %.c
	gcc -o $@ -Wall -std=c99 $<

clean:
	rm -f $(EXES)

oob.c

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {

  double nums[100];

  for (int i = 0; i < 5; ++i) {
    nums[i] = rand() / (float) RAND_MAX;
  }

  return 0;
}

strings.c

#include <stdio.h>
#include <stdlib.h>

/* ------------------------------------------------------------------------- */

/* int strlen(const char *s) { */
  /* for (int i = 0; i <  */
  /* int i = 0; */
  /* while (s[i] != '\0') { */
    /* i++; */
  /* } */
  /* return i; */
/* } */

/* ------------------------------------------------------------------------- */

int strlen(const char *s) {
  const char *ps = s;
  int i = 0;
  while (*ps != '\0') {
    i++;
    ps++;
  }
  return i;
}

/* ------------------------------------------------------------------------- */

int main(int argc, char **argv) {

  char name[] = "Jeff"; 

  /* name[0] = 'J'; */
  /* name[1] = 'e'; */
  /* name[2] = 'f'; */
  /* name[3] = 'f'; */
  /* name[4] = '\0'; // name[4] = 0; */
  /* name[4] = 'a'; // name[4] = 0; */

  printf("name: %s\n", name);
  printf("strlen(name): %d\n", strlen(name));

  return 0;
}

stack.h

#ifndef STACK_H
#define STACK_H

struct stack_t {
  int elements[100];
  int top;
}

struct stack_t *make_stack();

// Add element to stack
void push(int new_thing);

int pop();

int peek();

#endif

stack.cpp

#include "stack.h"

struct stack_t *make_stack() {
  struct stack_t *new_stack = malloc(sizeof(struct stack_t));
  new_stack->elements = ;
  new_stack->top = 0;
}

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