Demonstrate four string.h functions

LAB B02 · 01

Understand the task.

Aim: Demonstrate four string.h functions.

Review the related theory in Unit 3.

LAB B02 · 02

Know what goes in and what comes out.

Two text lines, each at most 40 characters. Empty lines and spaces are allowed. The joined output directly concatenates the two strings without inserting a separator.

BCA
Notes

First length = 3
Second length = 5
Copy = BCA
Joined = BCANotes
Comparison = first comes before second

Source programs read the documented input directly, without prompt text, so the same sample works in the embedded compiler’s STDIN field.

LAB B02 · 03

Plan the steps before writing code.

1. Read the first and second lines with bounded fgets. Remove their newlines and validate lengths.
2. Use strlen to measure each string.
3. Use strcpy to copy the first into copy.
4. Use strcpy and strcat to construct joined.
5. Use the sign of strcmp to report lexical ordering or equality.

LAB B02 · 04

One complete program. Ready to run.

#include <stdio.h>
#include <string.h>
int main(void)
{
    char first[42], second[42], copy[41], joined[81];
    int comparison;
    if (fgets(first, sizeof first, stdin) == NULL) { puts("Enter two text lines."); return 1; }
    first[strcspn(first, "\n")] = '\0';
    if (strlen(first) > 40) { puts("Use at most 40 characters per line."); return 1; }
    if (fgets(second, sizeof second, stdin) == NULL) { puts("Enter two text lines."); return 1; }
    second[strcspn(second, "\n")] = '\0';
    if (strlen(second) > 40) { puts("Use at most 40 characters per line."); return 1; }
    strcpy(copy, first);
    strcpy(joined, first);
    strcat(joined, second);
    comparison = strcmp(first, second);
    printf("First length = %lu\nSecond length = %lu\n",
           (unsigned long)strlen(first), (unsigned long)strlen(second));
    printf("Copy = %s\nJoined = %s\n", copy, joined);
    printf("Comparison = %s\n", comparison < 0 ? "first comes before second" :
           comparison > 0 ? "first comes after second" : "equal strings");
    return 0;
}

gcc B02-string-functions.c -o program

LAB B02 · 05

Connect each statement to its purpose.

• strlen returns size_t and excludes the null terminator. With these small bounded lengths, casting to unsigned long supports C90 printing via %lu.
• strcpy copies the terminator too. copy has room for 40 characters plus one terminator.
• strcat appends to an already terminated destination. joined has room for both 40-character inputs plus one terminator.
• strcmp compares character values lexically. Only negative, zero or positive meaning is guaranteed, not an exact result of -1 or 1.
• strcspn is used additionally to locate the newline for removal. No nonstandard strrev or strcmpi functions are required.

LAB B02 · 06

Follow the sample calculation.

LAB B02 · 07

Check more than one input.

Time and storage

O(L1 + L2) time for bounded input strings, and fixed arrays sized for the documented limits.

Start with the sample, then test a boundary and a case that changes the result. A correct sample alone does not establish that every input is handled correctly.

LAB B02 · 08

Use the real C compiler.

Choose an example and load it into the embedded C compiler. Select I/O inside the compiler, check the sample STDIN, and press Run. Change the input or edit the source to explore a different case.

BCA
Notes

First length = 3
Second length = 5
Copy = BCA
Joined = BCANotes
Comparison = first comes before second

#include <stdio.h>
#include <string.h>
int main(void)
{
    char first[42], second[42], copy[41], joined[81];
    int comparison;
    if (fgets(first, sizeof first, stdin) == NULL) { puts("Enter two text lines."); return 1; }
    first[strcspn(first, "\n")] = '\0';
    if (strlen(first) > 40) { puts("Use at most 40 characters per line."); return 1; }
    if (fgets(second, sizeof second, stdin) == NULL) { puts("Enter two text lines."); return 1; }
    second[strcspn(second, "\n")] = '\0';
    if (strlen(second) > 40) { puts("Use at most 40 characters per line."); return 1; }
    strcpy(copy, first);
    strcpy(joined, first);
    strcat(joined, second);
    comparison = strcmp(first, second);
    printf("First length = %lu\nSecond length = %lu\n",
           (unsigned long)strlen(first), (unsigned long)strlen(second));
    printf("Copy = %s\nJoined = %s\n", copy, joined);
    printf("Comparison = %s\n", comparison < 0 ? "first comes before second" :
           comparison > 0 ? "first comes after second" : "equal strings");
    return 0;
}

LAB B02 · 09

Explain why the program works.

LAB B02 · 10

Build the next skill.

Read the viva answers, try the extra cases, and return to the lab index to mark this exercise as practised.