strcmp
- C course
- Beginner
- Lesson 63/116
- 5 min
Learn to compare two strings with strcmp.
Comparing strings with strcmp
You cannot compare two strings with ==; that compares addresses. Instead, use strcmp.
int result = strcmp("apple", "apple");
/* result = 0: equal */
int diff = strcmp("apple", "banana");
/* diff < 0: "apple" is smaller */strcmp returns negative, zero, or positive. Zero means the strings are equal. Comparison is based on ASCII values of characters.
ASCII ordering
strcmp compares based on ASCII values of characters. Uppercase comes before lowercase: 'A'=65, 'a'=97. So strcmp("Apple", "apple") returns negative.
strcmp("Banana", "Banana"); /* 0 */
strcmp("Banana", "apple"); /* negative */
strcmp("apple", "Banana"); /* positive */The comparison is case-sensitive. To test equality, check if the result is == 0.
Practice Compare two passwords
Define two char arrays: "pass123" and "pass123". Compare them with strcmp and print the result with printf %d. The result should be 0; output should be 0.
Starter code
#include <stdio.h>
#include <string.h>
int main(void) {
/* define two char arrays */
/* compare with strcmp and print with printf %d */
return 0;
}Sample solution
#include <stdio.h>
#include <string.h>
int main(void) {
char a[] = "pass123";
char b[] = "pass123";
int r = strcmp(a, b);
printf("%d\n", r);
return 0;
}Expected output
0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 strcmp return values
| Term | Meaning |
|---|---|
0 |
strings equal |
negative |
first is smaller |
positive |
first is larger |
== |
compares addresses |
2 What does `strcmp("apple", "apple")` return?
int r = strcmp("apple", "apple");- -1
- 2
- 1
- 0 Correct answer
Explanation: strcmp returns 0 for equal strings.
3 Equality test
if (strcmp(a, b) ____) { /* strings equal */ }if (strcmp(a, b) == 0) { /* strings equal */ }Explanation: strcmp returns 0 when the strings are equal.